Pagination Duplicating Values in RecyclerView in MVVM

I am new in Kotlin MVVM also, I tried to achieved Pagination with legacy approach and stucked in a issue with my RecyclerView, whenever I scroll it the data duplicated, I tried DiffUtils but no help.

I Logged the data in VIEWMODEL class the data is not repeating but, when I logged in Activity where I am observing it is showing duplicate values

SEARCHRESULTACTIVITY.KT

class SearchResultActivity : AppCompatActivity() {
private lateinit var layoutManager: LinearLayoutManager
private lateinit var recyclerView: RecyclerView
private lateinit var pullAdapter: CustomAdapter
private var pageNumber = 1
private var totalItemsCount = 0
private var firstVisibleItemsCount = 0
private var visibleItemsCount = 0
private var previousTotal = 0
private var loading = true
private var fillPullList: ArrayList<RepoPull> = ArrayList()
private var userName: String = ""
private var repoName: String = ""
private var isEnd = false


override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    initialize()

    getDataPull(userName, repoName)

    loadNextData()

}

private fun initialize() {
    setContentView(R.layout.activity_search_result)
    recyclerView = findViewById(R.id.repoRecView)
    layoutManager = LinearLayoutManager(this)

    getSearchQuery()

}

private fun getSearchQuery() {
    userName = intent.getStringExtra("owner").toString()
    repoName = intent.getStringExtra("repo").toString()
    populatePullRv()

}

private fun populatePullRv() {
    recyclerView.addItemDecoration(DividerItemDecoration(this, DividerItemDecoration.VERTICAL))
    recyclerView.layoutManager = layoutManager
    pullAdapter = CustomAdapter(this, fillPullList)
    recyclerView.adapter = pullAdapter
    progressBar.visibility = View.VISIBLE
}

private fun loadNextData() {
    recyclerView.addOnScrollListener(object : RecyclerView.OnScrollListener() {

        override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
            super.onScrolled(recyclerView, dx, dy)

            val mLayoutManger = recyclerView.layoutManager as LinearLayoutManager
            visibleItemsCount = mLayoutManger.childCount
            totalItemsCount = mLayoutManger.itemCount
            firstVisibleItemsCount = mLayoutManger.findFirstVisibleItemPosition()

            if (loading) {
                if (totalItemsCount > previousTotal) {
                    previousTotal = totalItemsCount
                    pageNumber++
                    loading = false
                    progressBar.visibility = View.GONE
                }
            }
            if (!loading && (firstVisibleItemsCount + visibleItemsCount) >= totalItemsCount) {
                getDataPull(userName, repoName)
                loading = true
                Log.d("PAGE", pageNumber.toString())
            }


        }

    })
}

private fun getDataPull(username: String?, reponame: String?) {
    val myViewModel = ViewModelProviders.of(this).get(PullVM::class.java)

    myViewModel.endofList.observe(this, {
        if (it == true) {
            isEnd = true
            progressBar.visibility = View.GONE
            Toast.makeText(this@SearchResultActivity, "All PR Fetched", Toast.LENGTH_SHORT)
                .show()

        }

    })

    myViewModel.status.observe(this, {
        if (it == false) {
            showError(getString(R.string.no_net))

        }
    })

    myViewModel.getPullDataFromVM().observe(this, {

        if (it != null) {
           listRepos(it)  **//DUPLICATE VALUE COMING**
        } else {

            showError(getString(R.string.nothing_found))
        }
    })



    myViewModel.getPullList(username.toString(), reponame.toString(), pageNumber)

}

private fun showError(s: String) {
    progressBar.visibility = View.GONE
    val theView =
        this@SearchResultActivity.findViewById<View>(android.R.id.content)
    Snackbar.make(
        theView,
        s,
        Snackbar.LENGTH_LONG
    ).show()
}


@SuppressLint("NotifyDataSetChanged")
fun listRepos(repos: List<RepoPull>) {
    if (!isEnd) {
        progressBar.visibility = View.GONE
        fillPullList.addAll(repos)
        pullAdapter.notifyDataSetChanged()
    }
}}

PULLVM(View Model).kt

 class PullVM : ViewModel() {
var pullList: MutableLiveData<List<RepoPull>>
var status = MutableLiveData<Boolean?>()
var endofList = MutableLiveData<Boolean?>()

init {

    pullList = MutableLiveData()
}

fun getPullDataFromVM(): MutableLiveData<List<RepoPull>> {

    return pullList
}

fun getPullList(ownerName: String, repoName: String, pgNo: Int) {

    val retriever = GitHubRetriever


    val callback = object : Callback<List<RepoPull>> {
        override fun onFailure(call: Call<List<RepoPull>>, t: Throwable) {
            status.value = false
        }

        override fun onResponse(
            call: Call<List<RepoPull>>,
            response: Response<List<RepoPull>>
        ) {
            if (response.body()?.size == 0) {
                endofList.value = true
            }
            if (response.code() == 404) {
                pullList.postValue(null)

            } else {
                status.value = true
                val repos = response.body()
                if (repos != null) {
                    pullList.postValue(repos) 
                }
            }
        }

    }

    retriever.userRepos(
        callback,
        ownerName,
        repoName,
        pgNo
    )
}