Was Zumminer a scam?
Very likely yes. In future if you are willing to spend your money in mining, get your own mining rig even if that seems non-feasible, or best thing is to just buy and hold BTC for long term for a nice gain. These mining contract selling sites and so on that promise gains are nothing but ponzis.
I can´t log in and they don´t answer.
Of course you cant, because the owners have run away and are possibly running another few scams. Rinse and repeat, that is how they make money.
![Tongue](https://bitcointalk.org/Smileys/default/tongue.gif)
Its better to write the money off as a loss and continue on.