MTN Customer Diserice

I have had numerous (currently 3 contracts) with MTN for over 20 years now. Though I find their network coverage excellent it seems they lose track of agreed payment terms for cash clients and from time to time will suspend my lines because I have not paid my bill 15 days before the agreed payment date (note that my account has never been unpaid in over 20 years). I am currently in this situation with them and cannot get any help via their "customer service" centre or email. All 3 lines suspended for outgoing calls while I wait for MTN to either realize their mistake or until month end when I pay on the AGREED date. One would swear I choose to pay an expensive cell phone bill month in and month out because it is a nice to have!