I spent 5 years in total as a student, Gawd help me, and had a fair few 'run-ins' with College and University records offices.
If the university helpdesk service has confirmed that you "[i]don't appear to have submitted it[/i]" [u]bear in mind[/u]: if ALL the students had used an Open Office file extension, the helpdesk service might not be able to confirm or find ANY OF THEM!!
Academics are not always the brightest of the bunch!
I would advise that you (a)immediately re-submit in the correct format (although the 'portal' may now be invalid); (b)submit a hard copy to your tutor; (c)continue to pester the helpdesk service - ask them directly what they CAN and CAN'T see (as opposed to confirm).
If your campus has a Computer Faculty, ask around the computer technicians, they'll probably find your submission in a matter of seconds (if you did submit it).
Submission of files in the wrong format CANNOT be held legally to be non-submission, I would think at most it would be a 'slap on the wrist' and perhaps a salutory lesson for the rest of your life. A de-merit might occur but that WOULD be your fault.
Pester, pester, pester until you get fed up - not them.
And don't apologise for basic IT skills: I know someone with stronger skills (oddly attached to my fingers!) who has made similarly stupid, obvious, mistakes.
Never put yourself down - there are plenty of others around that'll try to do that for you!! :)