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.
Its better to write the money off as a loss and continue on.