Take money for phones I don't have

I took out a contract with Mondo for MTN. They told me I could send back the phone if I am not happy within 10 days. So I opened the phone and the quality was not good. I had no problem to send it back. I phoned them 7 days later and they confirmed that 7 days past and they will do the cancelation and won't deduct. Last night the deducted the whole amount. I feel this was very unprofessional and it is unacceptable!