Mtn lacks in customer centricity and communication

I've received the worst service from Mtn and their agents. I took up a contract with Mondo who falsely skd me a device I didn't need ,I returned to mtn I never used it as it was not what I wanted. This happened in February.Monda had a backlog of cancellation and I had to call in daily to request cancellation. Mtn kept collecting monthly with no communication been the 2 companies and listed me a bad payer on the credit bureaus,up to date I'm still calling mtn for paid up letter, I've been sent from post to pillar getting so much attitude from Mtn agent, they have been logging my request incorrectly because they care less as the contract was taken from Mondo. I start requesting for my paid up letter on the 22 September only to be told I need to pay in more money in top of the the R1300 I already paid for something I never used. This has affected my credit scoring for 3 months ,I can apply any funding to enhance my business as I'm viewed as a bad payer yet I returned the device within the cooling off period. I have noticed that these 2 companies have no working relationship and the attitude comes from Mtn as 1 agent once told me that whatever contract under Mondo I must just bare in mind that it's at my own risk yet they claim to be working with eachother. I'm lossig on a lot money waiting for the laid up letter