Rest between working days issue

I work Saturday, Sunday and Monday nights in a supermarket, 10pm - 6am. Christmas eve falls on a Sunday, and I was told I could either book it off or work 2-8pm. I go to book it off, and a new line manager says he won't approve any December holiday. So now I'm working 2-8pm following a nightshift, which I haven't agreed to and would be near impossible as I require a good 8 hours of sleep to function.

Having looked on the ACAS website, they state:

"By law (The Working Time Regulations 1998), employees and workers have the right to [...] 11 hours' rest between finishing work and starting work."

"Night workers must not work more than 8 hours in a 24-hour period on average."

However they also state:

"An employee might need to work through their rest entitlement. This should not happen regularly and the employer must have a valid reason for it.

If an employee has to work when they're supposed to be resting, the employer must still make sure the employee gets 'compensatory rest'. This means they take their rest later or in a different way."

My question is, what counts as compensatory rest? If that counts for the 2 hours less on the shift, would that still apply if the shift was 8 hours long? Also if I refused to work it, do I have the legal grounds to do so? And would my work still pay me? Finally, is there anything I could say about being previously given wrong information (about booking it as holiday) to leverage to get it as holiday?

Thank you!