Help

A month ago, I recieved a check from a investment company in the amount of $8,4334.76 in my name. I taugh it was from an account that I opened when I was younger and forgot about it. I called and emailed the company informimg them that I had the check and to ask them was it rightfully mine, but answer or reply. So I call CitiBank, which was the bank the account was held and the rep said that the funds were available. So I decided to hold the check for 10 more days until I heard something from the investment company but still no reply. I call CitiBank again to confirm the check and again they said the check was good. That monday I desposit the check and in 6 days the check cleared. I took out some money so I could do some christmas shopping and in 15 days or so they said that the check was no good, froze my account locking my direct deposit for work with it and know saying I have to pay that money back. I still to this day have not heard anything from that investment company. What can I do about this because I don't want any charges brought against me for this.
Thanks