theft of airtime

vodacom debited my husbands account for BIS service and never renewed it, after 2 days of arguments they claimed that the R59 was for internet charges. 2 days later he noticed his R100.00 balance had gone to R0.00 in less than an hour although he still has valid BIS. after more arguments with the call centre they claim it is for internet charges, but last month he downloaded around 4 movies using only BIS and his data never went down. Vodacom is full of excuses and provide a terrible and slow service! This is not the first time large amounts of airtime have suddenly disappeared with no explanation.