Strange iPhone call issues

[eamon]

Good afternoon, I have got a very strange problem that I'm hoping someone may be able to help with. I have an iPhone X and my wife has an XS Max. We are both on Three. When either of us call other people everything is fine but if we call each other it can be fine for a period and the on one or both phones it can sound like the other is in extreme winds or under water, or even stranger while on the call one will get the 'it has not been possible to connect your call' message and the call is dropped! We have had apple check both phones and also both had the sim replaced but the problem still persists! It's driving me crazy but I really don't know what to do. Can anyone please suggest something to try? Many thanks

 

[psychopomp1]

Does this occur when the phones are using wifi calling? if so, switch WC off and see if that helps. It could be that there's an issue with Three's WC servers or your wifi connection is weak.

 

[eamon]

Does this occur when the phones are using wifi calling? if so, switch WC off and see if that helps. It could be that there's an issue with Three's WC servers or your wifi connection is weak.

Thanks for the reply. Initially I did think it could be wifi related as it seemed to be much worse when on wifi but it happens all the time now we are on the road a lot. It's very odd and very annoying! I did wonder if it was to do with them upgrading masts to 5G at the moment but I still can't work out how it would only affect the 2 phones calling each other