3G sim card in 4G phone

[PRB48]

I have an O2 Classic Pay as you Go sim card. It was originally in a 3G phone but has been transferred to a new 4G phone, where it works all right at present but when making calls the screen says 3G even though the phone itself is 4G.

I get messages from O2 saying that the phone will not work after 3G is switched off, and telling me to buy a new 4G one, but I have already done this. It is the sim card that appears to be the problem, not the phone. What should I do to correct this? I need to keep the existing tariff and phone number.

[Enlli]

You can ignore the letter from O2 as they are sending them out to most people with old PAYG style accounts.

The reason your phone drops to 3G in making calls is that O2 do not allow 4G Calling (VoLTE) on PAYG accounts. That does not seem to be changing any time soon. What will happen after 3G closure is the phone will drop to 2G when calling.

4G data will work as it does now.

In your case you do not need to change your phone at this stage