Service Delivery Not Delivered As Promised

<p> I receieved an sms to get my phone upgrade beginning of the month of April, i went to fetch my phone and three weeks later the phone got damaged and till this day i have no idea what went wrong. I took the phone back to the store where i bought it and was told it would be ready in 7 working days, remember... This was in April. I kept going back to the store to check if my phone was ready or not, and to my surprise, it is already June and i still haven't gotten my phone back, and these people keep saying they're working on it to be sped up but i don't believe that is true, i haven't had a phone for close to two months now and i don't know what to do anymore. Please kindly help me, you are last hope, or else i'm gonna do something terrible to the workers at MTN because my patience has run out now! Thank you in advance</p>