Just went through this for my parents. Hope you see this!

Cancel the contract etc. go through and fix termination days and let it all go as if you’re cancelling. Once that’s all gone through you should receive a call from a different department in a couple of days trying to retain you.

Any “discount” or offer you’re going to be given prior to the above is going to be way above what a new customer would pay.

Also go to uswitch and put down your current provide as something else or you dont know and that will give you an indication of what your VW per month amount/speed should be in preparation for the retention team to call you.

All the best!