My account is block and got Abuse Complaint which says my server has attempted unauthorized access to other private system.. how do i proced

First complaint is as below:

To whom it may concern.

We have detected a hack attempt originating from your network from ip: <my IP>

This suggests that the above server has been compromised and is a participant in a botnet.

This means that this server has been hacked and now, in turn, is attempting to hack other servers on the Internet.

This IP address has now been blacklisted to protect our service from further brute force attacks. Furthermore, this IP address has been uploaded to DenyHosts’ centralised database. This means that this IP address will also shortly be blacklisted by any member who queries DenyHosts’ central database.