*** Account moved to debt collectors without informing me in a period of 1 month

I am truly not happy with the service received from cell C. I was on a data contract with them which i then cancelled and paid what was due to move to a prepaid contract as the value was better. In November 2021 i called them to cancel because I was moving to another service provider. They debited my money end of November and end of December becuase I cancelled my contract on the 12 which they only informed me about after I enquired. Customer service was supposed to inform me that they will debit it twice because I cancelled In the new month. When they took the second debit in December I was not sure why do I put a dispute with my bank and stopped the debit order because I had cancelled In November. After having done that i called them and they explained the procedure and i was fine with that even though I was mad because they hadn't told me before hand. I requested to pay manually since i stopped the debit order and needed their banking details. They said they would send it to me but i never received them I had to call 3 times to get the banking details. In the meantime they sent over my details to the MBD which is debt collectors without informing me and so when these people call me i had trust issues becuase i wasnt sure why they have a different amount for me to pay with different banking details (though i wasn't able to pay R250) but all i needed was banking details. When I got the banking details the third time around i paid what they said i owe and nobody informed me the the MBD was still gonna call for other money on behalf of cell c becuase they had given them my account. My credit score went down 21 points all because of this (R250 which i could have paid first time around after saying I'm not receiving the banking details) honestly cell C how does this work now? Is this how you handle accounts?