7 weeks and failing to repair handset

I have booked my Sony Xperia Z5 Premium in for repairs under warranty, in November 2018. To date the handset is still in the MTN store, awaiting collection by the Sony repair centre, 7 weeks later.

Every week there are different reasons, the latest being that the courier company failed to collect, and of course now it is Christmas and everyone is closed. I tried phoning MTN head office, as well as customer care, to escalate, but to no avail.

Is 7 weeks a reasonable amount of time to assume this is not going to be repaired? If MTN fails to repair, they should replace (as a refund is out of the question, being a contract phone)?

The shop's hands are tied in this matter, and I am failing to escalate. Who can I speak to about this, with the authority to help me with a solution to this problem? Being a loyal customer for 6 years is evidently not enough to get a warranty honoured...