Altech has NEVER credited my data

I have had a contract with altech for years now. My dad got me the contract and everything has been fine with my upgrades in store, until last year when the head office called me and offered me an upgrade, which had R110.00 airtime 25 sms and a 100 mega byt data and accepted it. However they have never credited the data from last year May until date. Every time I call them they either deny or say they don't know anything about it, that's really frustrating me. PLEASE HELP.