If any of those payments went through or was being processed while you switched cards, thinking the card did not get accepted when it actually did, SE would see it differently and it might appear like fraud from their side. I see you checked your banks but did you check ALL transactions, canceled, processed, denied and attempted? They usually send through a 1 dollar verification transaction first and your bank should see even attempted transactions. Never heard of SE just freezing an account down without a reason of some kind.