A member reported that he went to Poland to try to unblock a card and, even so, employees at the Mbank branch said they couldn't do nothing.
Mbank is a scammish bank, nothing more, nothing less.
If you want your money you have to send emails complaining about them to all polish and european banking authorities and send a copy of every email you sent complaining to several emails from Mbank.
After a few complains, they will pay to give your money back, just to stop your complains.
A list of european and polish authorities and Mbank emails were publish on this thread (or on another one related, search for it).
I was able to get my cards working by filling some form. However I failed on my 1st attempt, because I visited a former BRE bank branch instead of true mBank. mBank has acquired 2 other banks and they're still somehow incompatible in certain things. IDK how about large cities, but in small ones the clerks don't speak English, so if you can't speak basic Polish, you might need an interpreter
