Failing to cancel contract

I have taken a contract with this organization in 2018, but within my call out period,i deicded to return the item,i was advised to visit one of MTN direct stores, however they didn't want to take the items as they are in high risk area and the value of the item was high,so i called Mondo to arrange for collection,indeed it was collected by DHL,since 2020 when i received my first from debt collection institute,it shooked me that they called me for MTN account,so i sent all the proof i had that time, ever since I never heard no body up until i got another call from a different institute,i lost the handset that had all the text,so i had to explain my self from different debt collector up to this far,trying to resolve this with mondo but am getting no where!!! This absolutely absurd, now they telling me i should produce courier reference number where do they expect me to get from an account of 2018 out of all resources that you can use to identify either the Item has been received and returned back to you, your organization booked an item for collection,and you telling me you don't have any record of it being received,you got to be kidding me.

What kind of process does your warehouse have for it not to make use of the resources available, I have been emotionaly destresed over this endless issue.

Organization failed to make sure that,as soon as they received the item they supposed to file for closer of contract,instead now your business is being ***********, inconsistent, inconsiderate and not applying any impathy for the traumatic experience your business put me through,being called by different debt collection institutes,over an item that i don't even use this is rediculous!!!!!