Just call the fillgrid function as follows .
Solution 1
FillGrid();
grdView.PageIndex = e.NewPageIndex;
grdView.DataBind();
Solution 2
Add the following code in Page index Changing
if (CustomersGridView.EditIndex != -1)
{
e.Cancel = true;
int newPageNumber = e.NewPageIndex + 1;
Message.Text = "Please update the record before moving to page " +
newPageNumber.ToString() + ".";
}