Sorry to hear about your problems.
I am surprised that a Customer Services Advisor told you that they could cancel your Sky contract, as I am sure Sky (and any other company) would insist on you cancelling it personally (for security and compliance reasons).
If you haven't received the letter you were promised, you definitely need to escalate the issue.
Regarding the bill amount (£85.40), does it include part-month charges?
If you need to complain in the future, you can use this link
https://help.virginmedia.com/system/...LATION_REQUEST
Click on "Fault with your services", then
click on "I have cable services", then
click on "I want to make a complaint" then
click on "Haven't found what you're looking for? NEXT"
which will give you the various methods of registering a complaint.