It seems there's at least 5 people now having problems with cards like that. I've just checked the cards that I use, they still work. mBank started blocking cards for other sellers 2 weeks ago due to suspicious activity (namely instantvcc), but they spared us, because we had some connections to the bank. But mBank is now opposed to the idea of people reselling their cards, which is a new thing.

KOREKTA SALDA - OBCIĄŻENIE - balance correction, usually that happens when incorrect fees were charged on your card some time ago or maybe some transaction got canceled.