Your best bet is contacting data recovery firm and use their help to recover your deleted data. Do not write any data on the drive that suffered data loss. Too much overwriting does hurt data recovery up to the point where there is no recovery possible.
You can, however, attempt the data recovery by yourself with data recovery software but if your lost data is vital to you and your business, i don't suggest doing that. You're better off using professional help.
Also, do keep backups of your files. For business use, the monthly backup would be absolute minimum. Weekly backups are much better while daily backups are optimal. There are plenty of backup programs that can back up all data, either on schedule or once it has been created.
If...