How can it take 4 months to resolve a billing enquiry

I've increased my bundle and MTN managed to never load this. Since then, they have kept on charging me at the higher rate each month. I've requested the billing to be resolved at least 5 times and have even been to their physical branches 3 times. This is not accetable service and ombudsman will be the next step so MTN I'll give you to close of business tomorrow.