No service iPhone 6 roaming in France EE

"No Service" message whilst trying to roam in France.

Paid for a booster package (on EE - by text - no reply text) but after a while get "no service" on 2 phones; iPhone 6 and 6 plus.

Switched phones on and off AND did a hard reset multiple times, reset cellular settings, I Get a signal (Orange F) immediately after hard reset - then "no service" after a random period of time (1 min to 30 mins?). Turned data roaming on and off, phone on and off, sim in, sim out, different sim from a different network (non UK sim), manual network selected (chose 3 different ones), automatic network selection, hard reset - SAME. iPhone 6 Bought in Apple Regent Street, UK and iPhone 6 plus bought in the Middle East.

I am abroad and this is very frustrating. All friends on holiday in the same location on other UK networks with iPhone 6 and iPhone 6 plus are getting service (signal) AND using data (They use company phones so aren't worried about the roaming off booster package charges!) I have "paid" (tried to, anyway) for data roaming and I have no signal - "no service" message when there is service in this location (I am standing next to 5 people with iPhone 6 's and 6 pluses with full signal), so I can't even receive a call or send a text. What is going on??? This has never been a problem before.

I think it's a phone problem and not a network provider problem due to the same issue occurring with a Middle Eastern SIM card.

I can get a signal when I turn off data roaming and do a hard reset and leave Data roaming off - BUT then I can't send messages or use the internet without paying extortionate rates to EE or the middle eastern phone company. Previously boosters worked ok with EE (got a text and just texted back etc). That was on iPhone 5 though. Also I could use a "data roaming" booster on my iPhone 6 plus (I think it was on the 6 plus anyway) with the middle eastern sim when roaming in other countries.

Could it just be a French thing? Is it a phone iOS problem? Am I missing something in settings? I have emailed EE but no reply yet (72 hrs max they say, so I'll be almost on the way home by then!)

Has anyone else had this problem and resolved it? Any ideas? Thanks.