capital adjustment when paying account.

I took contract phone with Telkom some years back. Was not able to pay due to financial problem. Last year I went to Telkom Clearwater wanting to settle my account and was advised that my account is being handed over with Debt-in company. So I contracted the company and they advised me that my account is R3000 and asked if I can pay the whole account was advice by call centre agent to wait as they will call 8ta to get settlement account buy in a mine time I should make payment of R400 of witch I did. Agent come back to me and say Telkom say I own them R8200 because of handset value. I didn't have problem and I made payment arranging to pay R1000 every month. Which I sis from end of August and I have being paying that till November and December I made payment of R2000. Every time when I want to may total money Telkom make capital adjustment of R900 if I ask for accountability no one is able to give me answers. I am frustrated as I want to close this account but Telkom is making it difficult for me to. I real need help dnt know what to do anymore. Plz help