Duplicate transactions complaint

I am seriously confused as to how a bank allows for duplicate transactions to go through and have the audacity to say my account has been overdrawn and I need to deposit funds when there were funds?

1, I queried the transactions that went through twice and I am told I need to wait for 72 hours for a resolution?

2. I need a clear explanation as to how this happened.

3. My account is a transactional account, what happens when you guys duplicate my debit orders resulting in missed payments on my credit history?

4. When are you guys returning my money!

Please respond to this with actual information that makes sense before I take this to all other platforms as well.