Unknown deductions for thr phone I returned

In late March this year, I signed up for a contract phone (SAMSUNG A5) with Telkom In Bellville. I therefore returned the phone without using it within 5 days. They gave me a cancellation letter. However, Telkom is billing me for this phone of I understand why. I went to Telkom in Bellville and Stellenbosch to resolve the issue. I was put through a call centre and spoke to the agent. A few month later, the issue was resolved, I received a call confirming a resolution of this matter. However, Telkom still deducted R750 form account and they still deducted R1500 and R2975 on Friday and Saturday if for what I don't know. I am so disappointed with this. This will affect my credit rating with the banks, transaction going out and cancelled in my account. Secondly, they don't even deduct on my pay day. What if there were no funds in my account??? Would they refund me if their debit order bounces?????