Replied. I'm already testing some safe methods of loading the cards, improper topping up is the main reasons of blocks.
Not entirely sure, because the same method worked 2-3 times before.
I think it's caused by using the cards in different (but not block listed countries)
It works 2-3 times and then kaput...
This is the true that the newbie vouches won't tell you.
There's no way around it unless this seller deals with it personally in the bank.