If you dont have access to your server logs you will need to contact you host so you can determine where the connection came from on that date and time. I believe thats the only way to check to see if it came from one of the developers or not.
You might also contact cpanel support or their forum to see if they can tell you how to trace that back using the logs. Their forum is really helpful most of the time.
Or you can just chalk it up to lesson learned and move on. Remember any time you give out that info, always change it as soon as they are done working. Never leave it the same.
I would also delete that email address you were using for yourself and make a new one. Reason why is that address has been flagged now, its better to just delete it.