Hey @coliveira2001 welcome to the Nextcloud community 
You posted a request in the support category. Unfortunately you ignored the template and a lot of information to help you is missing. Please edit your original post and add all required details like Nextcloud version, webserver type and version, os version, related log file content. Use the support template.
Without additional information the community members cannot help you.
meanwhile, try removing the deleted users user directory from the datadirectory of the web server followed by occ files:scan --all and the try adding that user again.
If I am right, user accounts become “deactivated”, if you “delete” them in the web-UI.
There exist user related occ commands
occ user:list
displays all users - even deactivated
Do a
occ user:info Test
and
occ user:enable Test
replace “Test” by the deleted user you mentioned above.
See: Using the occ command — Nextcloud latest Administration Manual latest documentation
If it does not help, a search in the Nextcloud database is needed, but there I cannot help.