Possible fraudulent activity and closure of account

Hello fellow redditors i am in need of advice and or suggestions.Due to an unexpected situation last week I had sold a few of my positions roughly about 15k and I converted it to USD and deposited into my bank account no problem. I went inside the branch(CHASE)(which I do often)as i know I cant withdraw that amount of cash through ATM fill out a form and gave them a reason as to why i am making cash withdrawal at that time no problem.They had me wait for about 30 minutes give or take and I got my cash and went on my way. Today i go to the drive through to get $400 from the ATM and I got a message saying transaction rejected I was like weird I know there are funds in that account. I go inside the branch and was told my account has been frozen and was being investigated WTF? Spoke to a manager of course and was told they were gonna reach out to me in less than 24 hours. I raised hell there but nothing happened. Anyone ever experience anything like that before? What should I do?