MTN INCOMPETENCE

I have airtime , which I want to convert to voice minutes. Every time I get to the stage where I say buy I receive a message " there was an error. Please try again later" Spoke to about 20 agents at the call centre of which all are totaly incompitent. "Escalating to the back room" must be a euphemism for " dumping it in the waist basket" Managers not available and does not return calls. 26 hours since first call and @MTN has not done anything about the issue