iPhone contact mobile numbers in wrong format

having some trouble with my mums phone! We have recently been to Greece, the sim wasn’t removed and no contacts were added. She has an iPhone 11 Pro and on IOS15.

However, now we are back all her contact numbers have changed to 000-000 000 00 and I cannot seem to find the setting to swap them back to the normal format. Whenever a contact calls it doesn’t register the number to the contact because of the change in format.

there is a few things I’ve tried -

1. Reboot

2. Network reset

3. To find dial assist (this isn’t an option on this phone to even turn off)

4. Change location from US to U.K.

im running out of ideas! Even when I change numbers to the 07 or +44, it changes back to 000-000 in a few hours.

please help me