Is it T-mobile, Orange Or EE you are with?
All three have separate T&C's over their roaming charges
"T-Mobile EURO Talk and Text Booster - £2 Per Day Roaming Minutes and Texts. Available to customers on T-Mobile pay monthly plans only. Consumer plans only. You can purchase a daily booster for £2 which will give you unlimited calls and texts to and from mobiles and landlines in Europe and selected countries, when roaming abroad in countries set out below (the ‘included countries’). You will need to opt in to the booster by calling 150 on your phone or by texting EUDAYTM to 441. If you opt-in to this booster once, it will automatically trigger each and every time you’re abroad in one of the included countries when you make a call, receive a call or send a text. You only pay for the days you use your phone to make a call, receive a call or send a text. Receiving a call when you are in one of the included countries will trigger the £2 charge, even if you only receive a call on a particular day but do not make a call or send a text. You will need to text EUSTOPTM to 441 or call 150 to remove the booster if you no longer want it."