Unknown number repeatedly on itemised bill

Hi, there’s a number that doesn’t exist it at which keeps reflecting on my itemised bill for a few months now, I have emailed CS who confirm the number isn’t active on the network but they can’t stop the number from reflecting on my bill. Resolution was I should block the number however I am not dialling the number so why should I block it especially when it doesn’t exist? Please fix this because it’s causing issues in my personal life. I have sent email queries twice with no joy.