Pathetic service!

I have upgraded my long standing contract Thursday 26 November with a Samsung A5. Phone gave problems that evening (rebooting, closing apps etc) so took the phone back first thing the next morning. Phone apparently could not just be replaced but need to be send in to check. Send phone in, phoned Friday 4 Dec to follow up, branch promised they will phone me back. No feedback. Went there myself and nothing was done about it since my call. When they looked on the system the phone wasn't even booked in!? Logged a new query and was advised to phone the call centre to help escalate. Did just that only to be advised that they have no authority over branch and branch must decide? Phoned branch again and was promised they will phone me back before 17:00. Nothing, phoned 16:55 and was again advised they will phone me back on Saturday morning. Nothing once again even after numerous promises. Phone at 13:30 and yet again NO feedback. I was then promised by the lady they will sort EVERYTHING out on Monday. Guess what? Phoned at 13:00 AGAIN, no feedback yet and now suddenly it can take up to 10 days?? Phoned was returned in 12 hours and no one is phoning you back and very bad attitude from staff