Mtn is failing its customers

I have existing contracts with mtn. Mtn has failed from December to collect debit order amounts as agreed on my contracts. Thereafter mtn soft locks my phone claiming I'm in arrears yet the amount sits in my bank account. I have to call them monthly to beg for phones to work and request them to collect the cash from my account. Currently I have tried calling mtn for 6 days to no avail. I am frustrated