Charged me for something i did not buy

Initially Mr Price charged me for R50 every month for a sim-card i did not know or use. i finally called in December to cancel the charge and they said they did nit refunding me the R250 they already took. now my January statement says i have purchased airtime worth R225 AND I DID NOT. WHAT IS WRONG WITH MR PRICE MYMONEY ACCOUNT. I AM SOO FRUSTRATED because they going to make me pay for something i did not use yet again. i cancelled the sim early december how can i have bought airtime from it again.