Replacement / repairs of a NEW but damaged Iphone

I upgraded my phone at the beginning of October (an Iphone). The phone was faulty and I returned it within 7 days. MTN did not replace the phone but sent it away for repairs. It has been over a month now and I have still not received it back. They are now sending it back to their store so that I can log out of my 'find my iphone'. This was originally one of the problems with the phone as I could not log out of my cloud and I kept getting log in messages on other accounts. Surely MTN Carnivall Mall registered the fact that we logged out of the phone in store prior to sending it away. I was always under the impression that if your phone was returned within 7 days then you would receive a new phone and not wait over a MONTH! and still not repaired !!!