account still not settled

On the 02/03/2015 I settled my Fin Choice loan the amount of R3612.15 and coming to my surprise on the 12/03/2015 I received an SMS from Credit Worx that Fin Choice has handed me over with the amount of R3400 and I told the guy who was assisting from Credit Worx Fabian that I already made a payment on the 02/03 and he asked me to fax a proof of payment to him ,which I did and I kept on receiving the phone calls that I need to make arrangement for payment of which I already made and on the 14/03 I received an sms that I Need to pay R3520.90 I don't understand what's going on ,are they trying to de***** me or what I need my money that I paid extra because they told me that R3400 was needed but I paid extra they not doing anything about refunding me they keep on sending me smses that I need to pay.