Cellular Data Suddenly Stopped

Hello,

I have an Iphone12 and my O2 celluar/mobile data service has been working perfectly for months. As of 2 days ago, my cellular service suddenly stopped working. I turned my phone on and off, tried removing the sim card and putting it back in, turned celluar data off and on, double checked all settings were on to allow data and verified my account is active with no past due balances. However, I’m still not able to access the internet, WhatsApp, Facetime, ect.  Any suggestions? Thank you in advance for your help!