Incorrect billing

Ref# *** and ***<br> <br> I opened two accounts with MTN Nicolway in April and requested that this account be soft locked once it reaches R150.00 each. I was advised that for both, I will only have to pay R1000, since it is soft locked and I will not be incurring costs for call because I will have to buy airtime, My account was blocked in September because I owed about R4000 each. I phone MTN to get clarity. I haven't received anything from MTN until today. What I don't understand is, the phone was soft locked at R150 and I had to but airtime all the time, then why is the bill so high.