As we're customers here, we can't tell you when your minimum term expires. Have you tried the Sky app? If not there, you may need to call unless you can find the emailed or written confirmation of when you signed up and work it out from there..
Note that if you're looking at broadband over the phone line, Zen uses the same Openreach infrastructure that Sky (and most other providers) does, so the speed to your router won't be significantly different with them.
