Language issues

I went to the grocery store. I always like to pay with card cause I hate coins. I packed my stuff and tried to pay with my card, but the clerk was pointing at this paper in the counter. I didn't bother reading it, I thought she was asking if I had a loyal customer card or something so I just said "não, não, não" (beautifully pronounced, of course). The woman just gave me a bored look and probably said something like "yes, yes, yes" and then I actually had to read the paper and it said that I couldn't pay with card if the value was less than 20€. Stupid new rules. And now I'm searching for language courses.