I had the same issue. Customer service said the same thing. I had called the bank first and they confirmed that it absolutely was not blocked by them. In fact, the $1 "ping" charges were posting to the account. Even further, my husband, who shares the same bank account as I do, and uses a visa debit card as well (with different numbers) went through fine, while mine did not. Yes, the funds were there.

This is NOT NOT NOT a "banking issue". There is something wonky with the payment system SE uses.

In the end, I had to purchase crysta (shocker: my debit card was good enough to use for that for some reason but not to pay for the sub via normal means).

I guess if SE doesn't want our money, we have the option of giving it to a gaming company that DOES want it. It seems they'd rather lose customers than acknowledge and fix the issue :/