We deleted a form so we could upload an updated version but somehow we lost all our published data, is there any way we could retrieve them back?
If your devices have the "Delete after send" turned off (the default setting) in ODK Collect you should be able to recover the data over USB from the devices themselves. Under "General Settings" > "Form management" > "Form Submission". You should also be able to see the submitted forms under "View Sent Form".
You should be able to use ODK Briefcase to pull data from ODK Collect:
https://docs.opendatakit.org/briefcase-using/#pulling-forms-from-collect
Also, sometimes you can update a form to make changes without needing to replace the existing form: https://docs.opendatakit.org/form-update/