Why is sky mobile charging me for roaming when I'm back in the UK?

[GeoffN]

I was in Spain and sky mobile correctly charged me £2 for the day I roamed on 6 December. I returned to the UK on 19 December and have used my phone for mobile data etc (all within my plan for no charge). However, when I made a call to a UK number on 28 December I immediately got a text message saying that data roaming had been reactivated for 24 hours and a charge of £2 was added to my bill. Sky has credited me with this £2 but cannot explain why it happened or more importantly cannot say it will not happen again next time I make a call. Any suggestions as to how I can stop it happening again? (I might add that I switched data roaming off on 7 December and it has remained off since then.)

[caesarome]

@GeoffN 

The £2 charge applies when you use mobile data, send a text message or as you have done here to make a call. The charge then allows you to access your usual package as if you were home for 24 hours.

[GeoffN]

..... but the point is I had been back in the UK for 9 days before I made the call from the UK to a UK number so no roaming charge should apply or have been activated.

[caesarome]

That shouldn't have happened, so is your phone set to Home as per this:

Apple:
Settings > Mobile Service > SIM Applications > Make sure this is set to Home

Android:
Sky Menu App or SIM toolkit > Roaming > Make sure this is set to Home

As for the charge all you can do is to report this to Sky on 150.

[GeoffN]

Thanks for your help Caesarome,

I have an iphone XR. When I go to Settings > Mobile Service > SIM Applications > there is no "home" There are just four options (which all revert to roaming. "(Primary roaming)", "Automatic", "Sky settings" and "Partner settings". In mobile data options Roaming has been set to off since 7 December. Since returning to the UK nine days ago  I have used mobile data and made calls via WhatsApp using 4G  without any problem. It was only when I used the phone itself to make a call that it triggered the £2 roaming charge. Sky mobile cancelled this charge as soon as I reported it but they cannot explain why it happened nor confirm that it will not happen next time I make a call.