Two iphones Unable To Make Calls

[Oldtone2nd]

My wife and I are in Spain and from yesterday when we tried to make any outgoing calls we get a message "the number you dialled is not yet assigned to a client". We can not make any calls at all not even 202.  Both phones on ongoing monthly contracts.   How can we contact O2 for help?  Online auto assistance useless.

[MI5]

@Oldtone2nd 

Some things to try:
Check data roaming is on in phone settings.
Manually search for another network
Turn off 5g
Change your data APN to "mobile.o2.co.uk"
Check with O2 whether you have a roaming bar on your account. Do this via social media
If you message O2 on Facebook ( https://o2uk.co/O2CFB) , Twitter ( https://o2uk.co/O2CTW) or Instagram ( https://o2uk.co/O2CIG) , they should be able to help.

[Oldtone2nd]

Thank you MI5 for your swift response yesterday.  I did try your suggestions but to no avail.  However following this we had to go out about 100yds down the road.  On attempting to show friends the problem the phones worked perfectly!!!  On return to our location the fault reappeared.  So I checked and tested some settings and found that on my phone VoLTE (under Mobile Data - Mobile Data Options - Voice & Data) was turned off.  I turned it On and the fault went.  I have never been into this setting before and don't fully know what it does but it certainly affects making outgoing calls.  (I can make the fault reoccur by turning it off).  Once again thank you for your help and thought you might be intersted in my findings?  No response from o2 yet.

[Enlli]

@Oldtone2nd If the fault disappears not far from your home it means there is no O2 signal in your house.

By using WiFi Calling you phone connects to the mobile network through your broadband connection rather than the local phone mast.

[Oldtone2nd]

Thanks Enlli.  We can see the mobile phone mast from here and the signal via Movistar, has always been full strength.  Would you advise having WiFi Calling turned On permanently?

[MI5 · Accepted solution]

@Oldtone2nd 

No problem keeping it on all the time.

Phone will just switch between whichever is the best signal.