Experian won't update incorrect payment history

I have been trying for months to get Experian to correct an incorrect payment history. My account shows as unpaid for two years but I have statements showing that payments were made and that I even received a clearance letter after settlement. I cannot understand how this information correctly reflects on other bureaus but experian/compuscan just cannot understand the concept of payments were not missed. It's like they look for excuses not to assist.