Billing invoices issue

I app**** for a contract online last year November the contract was approved, upon delivery they delivered wrong devices when I call them they advised me to return the device to the nearest MTN store which I did. On the first of December Summer mobile called me to re-capture the application since they delivered wrong devices. They cancelled the one that was done in November. Since then I have not received any devices. Suddenly am receiving billing invoices (BA***) stating that am owing R3618 currently am owing R3629. 94. Below is what I received from them this morning. In this case what should I do, I am so tired of this situation 😪😪😪😪

Y'ello! You won't be able to make calls until you pay R 3629.94, in-store or via your bank. Use billing profile BA*** as a reference. You can find the banking details on your invoice