With those speeds I would be on the phone to sky complaining, they should then schedule a BT engineer to come and look at the line between the BT cabinet and your house.
What speed do you pay for? Have you tried testing the speed with a phone or laptop over wifi? and have you directly plugged your PC into the router using an ethernet cable?
This is a useful site about broadband speed: https://www.which.co.uk/consumer-rights/advice/how-to-complain-about-your-broadband-speed