I also think it's best to try and do the right thing, even though the likes of CARS don't care.
They may continue to tell you the amount you owe is rising but that does NOT mean you have to pay them a penny.
Send whatever proof you want. It's unlikely to change anyone's mind but at least you're doing what feels right for you.
The thread will be here for you to update us but, ultimately, you will do best by simply ignoring ongoing demands and threats.
Don't touch them owe me £500 since January 2019 make excuse after excuse. Seem they always have software problems sending money out. Keep saying they will call back or email nothing been chasing it now for 6 mths the phone staff always have the same banter we will chase it up and get back to you then nothing!