In hindsight for you, if you were able to roam then your SIM was working fine. Trying to change from a working SIM to another SIM abroad, was an exercise in futility - and will almost certainly now result in you being offline until your return to the UK.
You've not said specifically what else it was that you tried, just that it was "everything"... one standard bit of troubleshooting is to manually search for local networks and then select each one in turn. Sometimes problems are network-specific & swapping resolves - if not, it at least eliminates a variable.
