Rule #1: Don't use Nicehash on a PPLNS Pool
ZEC is a relatively small/mid-sized pool considering hash and it was DDoS'ed throughout the whole last week - and now this thread, must be a co-incidence

However, there are always rounds with bad luck and rounds with good luck. If you're rented hash during a round of bad luck you'll for sure not get the return you'd expect as the round takes longer than expected (bad luck), rounds with good luck however will return more than expected - no one is complaining then

Since most pools are PPLNS now, renting rigs for a short period of time will always result in negative rewards because the pool calculates rewards from the shares submitted over the last X rounds - not just the last hour or so..
So in short: Nicehash doesn't work on the ZEC (or other PPLNS pools) pool over short periods.
Oh and considering support - I'm available through PM here, through IRC, through twitter and through contact forms/e-mails... If you can't reach me, the problem is 100% on your side.