You should consult with an attorney who professes to have expertise and experience in the field of criminal defense. John Kannin is a good one.
[Please note: this communication does not constitute legal advice, nor does it form an attorney-client relationship.]
If you "plead guilty when that happened", the prosecutor no longer has to find "any evidence of the accusation". I also do not understand how your "case was clear" if you pled guilty.
What you need to do is get all your court documents and any other documents you can find regarding your case (and any other criminal cases in which you were involved) and consult with an immigration attorney to get an opinion of your "chance to get cancellation of removal approved".
Besides the specific facts of your criminal history, you need to meet statutory requirements to not be removed from the US.