Over charged

So I have been with Mtn since 2013 if I remember correctly, So in April 2015 I upgraded my phone and in October 2014 I bought my tablet from them, both on contract. So last year February I went under debt review and both contracts were suspended and the remaining 15 months contract on my phone and 7 months on my tablet were listed under my debt review payment. I phoned them yesterday 29/11/2017 to find out what my balance is due to my credit report stating that I am in a credit of R763 with them and they notified me that I still owe R7725.73! Now according to my calculations I have paid them R4640.83 on my tablet before I went under debt review and R4311.00 on my phone, I have also paid them R3660.37 up to date since I started debt review, so that gives you a total of R12612.20 that I have paid them in total so I want to know how I am still owing R7725.73 when the only payments I can see allocated from legal side is what I have paid through debt review thus far? This is ridiculous and I need answers because according to my knowledge I should be paid up by now and be in credit with you guys. I need this sorted A.S.A.P