When the creditor is your bank, the account is often subject to a contractual term called the right to a "set off." This allows the bank to take money out of your deposit account when you become delinquent on a credit account you have with them.
Most people don't realize that they are subject to this set off until it happens to them. This right is buried in the fine print and the legal mumbo jumbo when you initially open the deposit account, usually long before you obtain the credit account.
It is completely legal & very common. You will want to have your checking & savings account at a different institution than where you have a loan or credit card for just this reason.
Hope this perspective helps.
Don't put money in a bank you owe money to! By Federal law, a bank cannot go and pay itself back on a credit card, but it can for any other kind of loan. (A credit union can pay itself back for a credit card, too.)
If you have honest debts you can't pay, you should talk to a bankruptcy lawyer. That's the purpose of bankruptcy--that's why it's in the law.
It also sounds like you MIGHT have a Fair Debt Collection Violation from those debt collector calls. They cannot keep calling you if you tell them in writing to stop--or if you tell them on the phone to call your lawyer.
Some bankruptcy lawyers stay on top of Fair Debt law, too, and could help you in that area.