Hey
Sorry to hear your phones playing up
If it can't be fixed over the phone then the phone would need to go in for diagnostics.
No early upgrade or replacement* I'm afraid. It's in the Ts & Cs that a phone not working will be repaired by the repair centre under manufacturers warranty FOC unless something has voided warrant in which case there would be a charge.
*A replacement may be given if the repair centre can't repair the phone they will swap it for the same make and model unless out of stock. If out of stock a selection of same level handsets are offered.
A repair only really takes 4 days. Day 1 you send it, day 2 it's received and logged, inspected day 3, repaired, re-posted, day 4 received by you. The only thing that would day this is post or out of stock if exchange needed.