Mrprice blacklisting me for the phone that was not delivered to me

On July 2020 i recieved a call from mrprice consultant offering me a mobile phone contract sinse i have account with them, and i agreed. The phone was supposed to be delivered to my house, on the day of delivery, ram guys phoned me but unfortunately i was not in my house i was in town so they went back with the phone of which it was never delivered to me again.

I traced the parcel via the link sent by ram and found out that the parcel was returned to the shop, later i got messages that my account was handed over, and i rep**** and told them that i never recieved the phone and they promised to investigate the issue.

But again im getting messages that my account has been handed over to debt collectors and i need to pay via them. Im so fustrated because mrprice is careless, why are they charging me yet they recieved the phone back???

Pls help me what to do to deal with them or even sue them so that they can be careful next time and stop blacklisting our names for no reasons.