Unacceptable customer service

I ordered a new contract via telephone on 7 December. The phone arrived broken on 14 December. I returned it to an MTN store on the 15th December and have been trying to get a replacement since that date. For two weeks I have been referred backwards and forwards between Monzo and MTN direct - no one seems to know who initiated the contract. It now appears to be MTN direct who are still not able to tell me the status of my query. I sent an email to MTN complaints on 22 December (ref ***), 28 December (ref *** ) and 7 Jan (ref ***) with only an autoresponse. I find this level of service and incompetence across divisions of a large Mulitnational unacceptable