Payments made not reflected on account.

I need to know why my account was handed over to ITC with an incorrect amount. I've been communicating with your contact centre regarding the payment in 2015. I have been paying this and to my surprise I get a call saying I owe you over R2044.00 of which the R1500 I have already paid? I am tired of calling in and speaking to your call centre agents who cannot assist me because your credit control dept. is not taking calls. You **** to ITC informing them that you have sent me my latest statement of which you didn't.I called on the 18th March and your agent confirmed that no statement was sent to me. please can the incompetence of your staff and the non-functional processes not affect my credit score I've been mailing my proof of payments to ur credit control dept why are those not loaded on my account. I need someone to contact me and tell me how you will resolve this. you need to contact ITC and give them the correct amount which is R544 I need to pay it and cannot do this until they have recalculated because I am definitely not going to pay additional interest calculated on the incorrect amount you handed over in February when the R1500.00 was paid in Nov already