Billing query

Contract stipulates one should cancel 30 days before (calander month) Contract was also signed 4 years ago and I’ve been a customer for the 4 years

Herotel expected me to remember that this was in the contract from 4 years ago and I needed to cancel before the 10th of September I called on the 23rd of September just before I left my previous apartment I got billed for October for a “service” hat was untouched Why must I be billed when I showed intent to cancel and didn’t touch the service