First you should read exactly what the contract says and how exactly they define "fast" and "reliable" in it, if they even do.
Fast can mean low response time (which is not exactly relevant to ping since you could be in the ISS), but also high transfer speeds. Having either of those is no guarantee for the other.
Reliable generally means uptime. Unless they have "99.9% uptime or your money back" in the contract, you're sitting duck.
And once you've checked that, check the law. If the law says you can't break the contract for the reasons you have, you won't be able to do anything. Of course false advertising may be a good case against the host, but you still have to take the law into account.