No network guarantees 100% service all of the time @Niknaks. This is covered in the o2 Ts & Cs that you agreed to as part of the contract.
You already know about the mast fault, so the help given in this guide Guide: How can I sort out my network issues? may not be of much help, but if there are other users on o2 in that location getting them to raise the issue on the My Network app will increase the rating for the fault.
You can look at WiFi calling (if available) but other than that there is not much else you can do...
Please note, this is not customer services and we cannot access your account. Do not publish personal details (email, phone number, bank account).
Link to our guide on how to contact them can be found here
