If an investigation results in you being suspended from work, a smart employer would typically issue a form for the employee personnel file that documents this fact. The paper or electronic form would be signed by the employee, supervisor, department manager, and HR representative to verify mutual understanding of the discipline. The Company may need to refer to it in progressive discipline or in an unemployment hearing should the employee's behavior not improve.
There may or may not be an overall case report. It depends on the employer's practices. You can ask whether your company follows this practice and request a copy, but you'll probably be told that Company documents are HR confidential and you don't have access to them. (Some states may let you see these, however.) Even if you do not have a report, when a case is closed, and it has been unsubstantiated you may want to request a brief email from the investigator saying that. Just ask whether s/he can send you a short email stating that the case has been closed and the matter is unsubstantiated. At least that documentation will make you rest easier. Managers change, HR reps change, and at least you'll have this to prove the result in case it's ever an issue.
Regarding your never being interviewed, typically a person complained about IS interviewed so s/he can present their side, but in rare circumstances, the allegations do not warrant an interview. For example, video or records clearly shows that the claim is unfounded.