This was a previous response to this question from VM:
"So what I found out about this "Cohort Charge" is that it was part of a discount before this years price rise in August. I can see it first appeared as £0.00 in June 2019 whilst our systems were getting ready for the increase, then in August the change was initialised but our systems have not recognised it and turned the discount into a charge of £1. The reason why it has done this is because you're on an old package and the best thing to do going forward, to avoid any further discrepancies, is to review your bundle.I would love to do this myself, however changing packages is out of our scope here on the forums. You can have a chat with our packages team on 0345 454 1111 option 1, 4 then 2. You can also use our text service on +44753 305 1809 if that's easier for you.I hope this makes sense for you, I'm sorry for any inconvenience or confusion that this may have caused, it was quite perplexing for us as well! But if you have any further questions I'm happy to answer them as best I can. "