Airtime dissapearing

Vodacom airtime that dissapears. My 90 yr old mom bought R220 airtime on the 14th July. She bought a further R220 on the 15th July. Both receipts I have in my possession. She phoned a person on the 14th July and spoke for 22min 46sec. I have record of her phone calls. Of the R440 airtime she bought she has R178.83 airtime remaining after one call lasting 22min. Vodacom better start explaining very quickly where the airtime went. I have documentation and photographed all the receipts and balances.