Why does my GridView control in c# aspnet display an old table below the new table?

The objective i'm trying to achieve is to display filtered data in the same gridcontrol. So what I do is e.g A-DROPDOWN clicked, display XDATA in GRIDVIEW1. Then FilterA selected, this filter calls the "ADROPDOWN" clicked event again and then checks the appropriate filter then passes the appropriate sql query, then displays "YDATA" in GRIDVIEW1. Now when I select B-DROPDOWN, ZDATA is displayed however below it is the YDATA. If I select C-DROPDOWN, VDATA is displayed howver below it is still the YDATA.

If I selected A-DROPDOWN then XDATA would be displayed then if I would selected B-DROPDOWN without selecting any of the filters, WDATA would be displayed cleanly in GRIDVIEW1 without any data below or above it. Would appreciate if anyone has any suggestions. Cannot show my code because its 20000 lines.

Would like to add. The alphabets assigned to the dropdowns and data represents the different datasets.