My drone fone I use 1P mobile.
Instead of a monthly charge its 3 months. What you dont use gets carried over. Its about £20/year. 1p per txt, mb, or per minute call.
Just google 1P mobile, they send you out a sim. No monthly fees, much cheaper than Giffgaff.
When abroad I,ve usually got so much data carried over, I can check my home cameras anytime.