We have certain rules established by the bank, which are clearly stated in this thread (
https://bitcointalk.org/index.php?topic=5484771.msg63647081#msg63647081), on our terms and conditions page, and through periodic notifications on our website. These notifications serve as a reminder that multiple declines due to insufficient funds may result in your card being deleted. Your card received a significant number of declines for insufficient funds and was therefore deleted by the bank’s risk control system.
I went through a similar thing. My card was first blocked (2+ months ago) and then deleted from my account a few days ago. Also, I had a negative balance on it, because fees were charged from the bank for some unexecuted transactions.
Honestly, I didn't see a problem with deleting a blocked card, which had a minus balance. A very small, but still negative balance. Now I can't remember how many notifications there were that it would be deleted, but I remember one for sure. Maybe in the future, you can implement some email notifications about such events. If the user was informed in advance about the scheduled deletion of the card, he might make a deposit and cover the required amount.