The short answer: an intro offer expired
If your Office 365 renewal has doubled, the most common cause is simple. You bought on an introductory price and that price has now reverted to the provider's standard renewal rate.
The intro offer was the bait. The renewal is the real price. Here is what the main UK incumbents charge once the intro period ends, all per user per month ex VAT:
- IONOS: £1 intro, renews at £13.50
- 123 Reg: £7.99 intro, renews at £13.99
- GoDaddy: renews at £15.99
Going from £1 to £13.50 is not a doubling, it is a 13-fold jump. Going from £7.99 to £13.99 is close to a doubling. None of this is a billing error. It is the pricing model working exactly as designed. The low number got you in the door, and the renewal is where the provider makes its margin back.
The licences themselves have not changed. You are paying a much higher price for the same Microsoft 365 you had last year.