You should be able to achieve this using SharePoint:
If you configure the Main Submit data connection to submit to the SharePoint document library with a static file name (not generated from form data), you can specify that the form overwrites a previous version if it already exists in the library. with a static filename, the form will always submit and overwrite the previous. You can also restrict options which are available to form users such as saving a copy of the form, which also forces users to submit, overwriting the required version.
You can also alter the permissions on the document library after the form has been submitted the first time to prevent any additional forms being submitted or any unauthorised changes to the forms data being made.
The following may be of some assistance:
Please let me know if this helps.
Thanks
Daniel