I am thinking two different things it could be, I had a problem last year.
My problem is this, I have a target credit card, with a $200 limit. I bought some cards say 4, went right over paid them off. The next week went in bought 4 cards, went over paid them off and continued this pattern for about 10 weeks. I got a letter from target saying that I was fraudulently using the card. Went to target to ask what it meant, no one knew. 2 hours on the phone and the answer is you can not build up your own credit. I am only allowed to buy $200 a month even if I am paying it off.
I do not have a target debit card but dd does. She bought a bunch of cards, she eventually got that she could only buy three more. She did not understand. Target said it was from her bank not them. She went to her bank and they had some kind of stop at $1000 to a store in a month, for fraud protection. She just asked them to up the limit to say $1500 in the month and she was fine.