Unable to Match Persian Characters from DropDownList in Sql Server Database in ASP.Net

Hi

I have 2 table in database 1-State  2-City and bind DropDownList  1-ddlstate   2-ddlCity from these table

and when I select item from ddlsate , according to my selected item from ddlState , ddlcity's Item  change I used OnSelectedIndexChanged for ddlstate

problem is:

I enter some data in tables with persian Alphabet now when I select some Item from ddlstate that contain these alphabet in persian  "ی ،پ،... " it didn't show any Item in ddlcity but when I select item that didn't contain above  alphabet it show item in ddlcity correctly why this happen?

Best Regards