What can I do if I still have not recieved the rights review from ACM?
They claim to have sent an email that you didn't receive? First, check your spam box. It's quite possible that automated emails sent by conference organizers get caught in that.
It that doesn't help, escalate to the program chairs. They accepted your paper, they want the publication process to succeed, so to make it hang on a rights review email that may or may not have been sent is not in their best interest.