A good idea which has been discussed before but there was some concern over security as the app would have to have your MyO2 open at all times.
There are widgets you can get on play store which will do the same thing though but you need to set your data amount and refresh dates manually.
I have no affiliation whatsoever with O2 or any subsidiary companies. Comments posted are entirely of my own opinion.
This is not Customer Service so we are unable to help with account specific issues.Currently using:
Pixel 7a (O2 & Lyca), One Plus 6 (Sfr), iPhone 12 Pro Max (Vodafone)