********* ******* banking rules lead innocent persons damaged

I am so disappointed and upset with this bank. Firstly I had an account with them 2017 being used as my salary acc. Then I decided to sell my phone and was contacted by someone and did a deposit into my account and said dey will pick the phone shortly. I did not think anything. A few hours later he called me to say hez not interested in this sale n wants his money back. So I sent the money back. I don't see my fault in any of this so maybe a day or 2 later I wanted to use my card n it said contact bank. I went to the bank and dey told me the account is on hold and cannot be activated because there was ********** activity. It was not told to me then that I should contact the buyer and get him to do an affidavit confirming the transaction so I can clear the account. No advice from the banking institute. So I went away. After 5 years I went to open an account and the status is still the same only this time they told me to contact the buyer and get the affidavit from him then only they will re activate the account. It was not my fault why am I being labeled as a *********. This is defamation of character. Firstly they are unhelpful and then they label me as a *****. This is unacceptable and I want to get legal advice for this.