Debiting without consent!!!!!!!!!

MiWay debited my account without my consent. I contacted them to query the debit whereby they responded that my premium has increased therefore they went ahead and debited the extra amount after my installment was taken. After investigating, they apologized for the mistake but they cannot credit me straight away. Basically they stole money without my knowledge and then telling me they cannot credit me. What's stopping them from taking money whenever and from whomever they want. This is unprofessional and I will be changing my service provider.