O2 doesn't work in Algarve?

[KJ2022]

Hi,  Every time I visit the Algarve (central/west) my phone doesn't work?  I can receive texts but I can't send texts, make calls or use mobile data?  I contacted O2 twice (in the UK and also whilst in Portugal) and they were unable to resolve my issue.  I changed to a newer sim card but it still doesn't work?  My other phone is ID mobile and that works fine.  Any ideas why it doesn't work?  (Samsung, android.)

[MI5]

@KJ2022 

Because it's PAYG which seems beyond the capability of O2 to make work abroad.

Many posts on here if you search.

[KJ2022]

OK thanks.