I don't know if there are any states with usuary limits anymore. Regardless of who you got it through, the card itself was likely issued from a state that has no limits. And they now have clauses to jack up your rates if you are late with any creditor on your record (not just them).
As banks and credit card companies merge into reduced competition, they are jacking credit card rates even for excellent credit into the 20% range. The best way to avoid falling into their trap is to make sure that you will have the money to pay any charges in full each month, before even using the card.