Lines suspended because of Telkom's own error!

Telkom employee Mahommed from Northgate shop made an error while processing upgrades on our account, instead of being charged monthly installments, we were billed R72 00 as a cash payment for all 3 lines. He attributed his mistake to system glitches and promised to rectify to and make sure service was not interrupted. Our lines have just been suspended because of Telkom's error and we keep being sent from pillar to post. We tried calling Northgate shop directly it goes to a call center which promises a call back which never happens. PLEASE HELP!