Bad service

On the 01:10:2014 Shapiro Shaik lawyers of MTN send me a message saying that I must call them due to my outstanding balance I have with their client I was surprised because I thought my ex husband was paying the account because it was the arrangements we make when I take the iPad on my account that is why I give them his bank account. Now every balance was on my name but MTN didn't call me first they just handed me to their lawyers without my concern anyway it happen when I call Shapiro Shaik they told me that I'm owing their client R3538. 18 I pay until I get upset on 01:04:2015 when they told me that my balance is not going down due to that I didn't't pay full amount so why they were saying I can make arrangements if The balance is not going down I stop for 4 months but I'm paying again something which doesn't go down I feel that is not fair please help me. The amount I'm paying every month is R200.00 .Even the balance they send on my phone it says R3752. 97 it's true doesn't go down all my money I'm being paying where is going?