disappearing airtime

I loaded my phone with R180.00 airtime on the 21/05/2015 at about 18:15 .With only 2calls made between then and now my airtime is finished.I also loaded separate bundles.When I call MTN They tell me I must call tomorrow as they are short staffed and cannot check on the system for me after I waited for 30minutes for the call centre to answer my call.If MTN is tired of being my pure refers provider they need to make this clear as this is not the first incident.every after 2 to 4 weeks I complain about the same issue and never gets resolved.I want my money back or airtime to be reimbursed immediately.