monthly suspension of line

After many years of no service issues with Nashua Mobile since January this year, when my account was transferred to MTN, I've had nothing monthly battles as my line gets suspended after they have debited my account. Having finally got an increase in my credit limit (by sms despite my request for a Managers contact details), they have now again suspended my line today due to the OLD limit being breached. It is clear that internally, one part of the business/system is not talking to the other. Does anyone have a senior manager/exec's email details at MTN so that I can get hold of a human being at MTN instead of sending emails to an unresponsive customer care centre who seem to be very good at flooding my inbox with heaps of useless sms's. MTN re-activate my cell phone!! ? am fed up with your complete lack of service having paid you and Nashua Mobile at least R1,200 every month !