Suspend line a 75% of credit limit

I paid the full amount on my account and then MTN suspended my line because there are R136 missing between what I paid in and what they received in their account. I spoke to a few people at the help desk as my lines where suspended 3 time in the last 2 weeks. I have send the POP to Lilian. Today my lines where cut off and on phoning the help desk I was inform that they suspended my line because I reached 75% of my credit limit and that this is standard practice.<br> <br> HELP!!!, can someone with sense and the ability to assists please resolve this.