@GM don't worry too much about your credit. you lost it.
I lost 116€ because I re-registered last week on the new Three app. The old app wasn't working anymore (they redirect you to the new app to see your balance and your plan expiration). Something went wrong and I wasn't able to login neither on the mobile nor the website. Now it is more than a week that I can't access.
I didn't receive any SMS from Three about the expiration of my plan or about my internet consuming (like it was happening before). So, long story short (thanks to customer service) we discovered (on April 15th) that my monthly plan was expiring on the 13th of April and I lost 116€ in 2 (TWO) days because of internet traffic. And, by the way, I'm stuck at home with Wi-Fi because of the lockdown.
What is happening is this: Three is upgrading its system and they had (and still have) massive issues during the transition. Unfortunately, customers like you and me that have our plan expiring during these days, are the ones that will take the hit and will pay for Three disservice.
Best of luck
