O2

Do I use old or new sim to text swap?

Ordered new sim as calls cutting out..received it many months ago from customer services..is it too late to try swapping it now or does it have expiry date?..and if I swap it how do I request my old number back..not changing provider or contract or a...

I will be switching from A40 to A41 which phone does the sim stay in for the transfer? or does it matter..have seen conflicting info so want to be sure..

As above list of stores in Belfast that still have gurus?