Getting back on topic one of the following is likely happening:
- You are attempting to register on a computer that another RuneMate user has previously registered on. Try creating the account on a completely fresh computer.
- Your IP/computer is flagged as spam, potentially because you have some malware on your computer that a hacker is using to steal your IP to do bad things. Run a virus scan like Malwarebytes (free) on your computer.
Try #1 first, but running a scan on your computer never hurts.
I have made some changes to the registration checks. Please try again.