Please let me leave!

[#1]

I recently changed from Plusnet Pro to Business Option 3 which started on the 2 September. After just one day I decided to change back to the Pro account because I wasn't made aware that Business Option 3 limits the use of video streaming in the evening. This all happened smoothly enough because of the 30 day cooling off period.
I then decided however that my only option is to leave Plusnet and find a business account that does not limit video streaming in the evening so ordered a MAC key. The key arrived today along with a warning that by using it I will be charged £452.43 cancellation fee!
I spoke to support who said that it's just the way the system works and that I would need to wait until 2nd October after I change back to Pro before using the Mac Key in order not to be charged this fee.
Surely this can't be right? I have used the 30 day cancelation period to change my mind, how can Plusnet legally still charge me a cancelation fee if I leave?
Paul.

[#2]

The large cancellation charges are because Business accounts come on a 12 or 24 month contract. However, we've made a special case for you and allowed you to leave with the standard 10 day notice cancellation.
To do this without breaking your billing I've returned you to Broadband Your Way Pro @ £19.99 per month, your cancellation charges will be calculated on this monthly charge. You can ignore the previous emails you have received but I'd recommend giving our Billing Team a call on 0845 140 0200 when you've migrated away to make sure your account is closed down on the correct billing terms.

[#3]

Blimey, thanks Ben!
I'm quite shocked because I was told on the phone that this was totally impossible!
Much appreciated.
Best regards
Paul.

[#4]

Glad to hear that I could help. Mind me asking which provider you're moving to?