The code is specific to the phone, so no-one else will have access to it. I can only assume you perhaps mis-remembered the new code and, yes, you have a limited number of attempts at it.
The only way to regain access to the device will be a factory reset, but that will delete all data (that's one of the reasons why it's so important to back up important info). Your emails, contacts and calendar should re-sync, but anything else will be lost. If you have anything on a sd card, remove that first so that it doesn't get formatted.
You could try contacting HTC to see if they have any ways in, but I doubt they do. Be ready to prove ownership if they are prepared to help.
