Cancelled router contract

Mtn called me offering me their wifi. It was delivered within 2 days. It worked and most of the time there was no network. Went to MTN cradlestone and they checked and showed me the reason i had poor network was because it was showing as if im in Krugersdorp instead of Kagiso. Well they fixed that. I reached home it was worse and i went back to mtn i told them i need to cancel they told me they will log a call. Went the third time they told me stories again and bear in mind i was still within the 10 day cancellation window. Forth time they took it and asked me to call mtn or email which i did. They then asked for SR number then i went to Mtn the guy who was assisting told me they were unable to generate it since it was booked to be checked. Then finally he got it and took a screenshot shot with my phone. I sent it via email snd they saud they cant see the screenshot then again i went to mtn and they wrote it for me. Now yesterday i received an sms for a debit order for the sane router that i returned. I need this to be sorted out coz i wont pay for something that was on and off. Ive got lots of OTP that i got when i was at MTn