Try the following:
1: Try logging in using a new account. You have probably already tried this but you didn't mention it in your post, and it's best to check. (Ignore if done)
2: Try logging in (On an unbanned/new account) using a VPN to mask your IP Address. They may have banned your IP Address from accessing the Crossfire servers, so try this because changing your PC's MAC Address will do nothing if you're still trying to connect to their servers using the same IP Address.
3: If step 2 doesn't work, try logging in from a different computer that you have not played on Crossfire with before, also use a VPN.
If step 2 works then all they've done is ban your IP Address and you'll just have to connect using a VPN whenever you play.
If step 2 didn't work but step 3 did, then they've blocked your computer from accessing their servers, and if they've done this then they will have most definitely banned your IP Address aswell, so you will have to play using a different computer, and a VPN.