I have two contracts.
I have a Three sim only contract that is in my router (it’s actually back on offer now). This is because they provide unlimited data, no caps or fair usage, it’s 5G ready and they actually allow you to use it as a hotspot. Don’t forget to claim your £70 cashback too.
And my phone contract is with EE 
Infact I just got my cashback the other day and used Monzos pay early for the first time 