EU Roaming - Calls to UK worked in Poland but not in Spain??

Hi all.

Just wondering if anyone can help me here, my SMARTY sim worked fine in Poland a couple of months ago, but when I was in Spain I was not able to make calls to UK landlines or mobiles, all other features worked fine:

Data Roaming - Fine

Calls to Landlines in Spain - Fine

Texts - Fine

Incoming Calls - Fine

Outgoing Calls to UK landlines or mobiles - None 😞

I go back to a different region of Spain in a few weeks so would prefer to have calls working if I can. I can't understand why everything worked fine in Poland, but then the calls issue in Spain?

If anyone can help I'd be very grateful.

Thanks