If you had a pre-sentence interview, or a recommendation for deferral from the probation department, they should have at least at one point had a record of your case -- and if it backs up your assertion that you had a deferred/conditional sentence, and they have no record of any issue post-sentencing, that should help a lot in terms of establishing what your sentence was supposed to be.

If you cannot find any records, as much as I hate to say it, you're in a bad spot -- and I think you'll end up needing the help of a lawyer.