I had an agreement for the first 6 months my subscription was £1, yet it’s gone up to £16.80 after just 3 months, why??

Hello hello-dorsetdiy-

Thanks for joining the Community. 

From checking the billing information on your account, I can see that this was activated using our 3 month 90% discount offer. Now that this has expired, you'll be charged the standard price (£14 + VAT) for QuickBooks Online Simple Start.