Raise a disconnection request and explain the issue to the retention team when you receive a call. They will be on their toes to solve this issue. I know it's not the most efficient way but trust me these ISPs are thick skinned now and just complaining won't get you anywhere.
This method has worked quite a few times for me.
It's not a customer's job to identify the issue and shouldn't be held liable for it. ISPs are just lethargic and their CC situation is well known. It's not like we are asking for a free service, we pay for it, so ISPs should actively work to identify the problem and resolve it.
"We won't budge until you threaten us to leave" is the mindset.