Overbilled after my contract was cancelled without my permission.

I had a cellphone contract with Mtn which i took as an upgrade Feb 2022. During the month of may i was called by a 3rd party company called Mondo to offer me an unlimited, uncapped WIFI MTN home router, which was reasonable for me and i accepted the offer and they delivered same month. After several attempts even getting help from mtn people over the phone the router never worked, and the Mondo people confirmed that its because of network issues they failed to check coverage first. They asked me to return the device and i returned it to MTN shop and i was given a reference number to give back to Mondo so they can cancel the contract, i did that and they promised to cancel and refund me. They debited for June, July and i got concerned now because i was being debited for something i am not using i followed up the matter over the phone with Mondo till they took me serious in August. And i was expecting a refund from the time they started debiting till August, only to find out instead of cancelling the WIFI router number they cancelled the cellphone contract number i always had, i saw a message on my phone saying i changed from contract to prepaid. I called MTN they Said it shows EARLY cancellation on their side which means i now owe MTN R16608 and the router is still active. I asked MTN to help me with the cancellation of the right number and reinstate the phone but they referred me to Mondo, i informed Mondo about the mistake they made and acknowledged it and adviced me to wait till they fix while i was waiting i was still debited and month of Sep passed i started showering them with calls even demanding to speak to the manager and they finally cancelled the router number on the 3rd of October and told me they lodged a ticket for refund. And when i asked about the cellphone contract number when it will be reinstated they referred me to MTN, MTN told me i must go to mtn shop to help them re instate i went last week friday and they lady who was helping me told me on her system she cannot see any communication about what i am saying to her all she see is early deactivation of cellphone contract and deactivation of router and it doesn't appear that i have any contract with MTN. she further said she cannot help me with reinstation automatically she will have to lodge a ticket. I was expecting that this month my premium will be less as now the router is cancelled i will only pay for the phone and its insurance and even get a refund but instead i was debited R16607 rands which is more than what i earn. My bank account now is on minuses, some of my debit orders bounced. I went to the bank frustrated they said only i can stop the debit order of mtn and my worry is i have been following this matter with MTN since May and i am sent to pillar to post, everyone tells me about lodging a ticket. So i do not know what am i going to do with a bank account of minus R17000. I never skipped payment or reversed payment as i do not want to make a bad name for myself but now what do i do with this situation?