As a former user of Mercatox I highly recommend you NOT to use it.
I've bought railblocks long ago and could never move them out - had to sell lower than market price (like 25% lower) and send btc because most of their wallets are permanently on maintenance (also I paid 20$ fee) to my wallet.
If you look up on almost any social it's full of people asking support but none of the team ever answers.

Stay away.