I was once about to leave a job I had and (this was long ago) we had computers, everyone was issued with one, but no internet connection. In my case I in fact had next to no use for the computer in my particular task-set - I occasionally played solitaire and drafted stuff for printing on paper (personal and work). Perhaps 5-6 weeks before I left all the non-white people suddenly started behaving oddly toward me, this was after I found the IT man studying my computer quite intently. Before I found my immediate boss using my computer - he was a bit flustered and said his was playing up, did I mind ? No said I.
I confronted one guy of Indian origin and he reacted with some discomfort, excused himself, and came back to tell me I should watch out for my immediate boss who had told him he intended to see to it that I would never again get a job with the firm.
I had not password protected the computer assigned to me (so far as I was concerned there was nothing on it I should be secretive about, no need) and, to show how naive I was/am, before leaving I never thought to search for planted stuff on the computer. It was quite some time later that I realised that almost certainly my boss planted something depicting me as a racist or something similar to that.
The reason for my assigning low importance to this was/is that the firm is a large multinational with a rotten internal atmosphere/culture and I would not want to work there again - the contracts are quite lucrative and sought after by a lot of people, not least established employees. My boss was perhaps insecure and saw me as some kind of threat (can't imagine why) and he would be among of those who clung onto their positions for dear life.
Like me, you possibly will not be able to find an effective solution to the fact that you have been smeared, it is uncomfortable knowledge whenever you think about it. The simple fact is that people seem on average to be more likely to support the negative than the positive, even if you know and everyone looking into the facts knows that this is malicious practice against a clean character who is the victim. This is likely a something that has been in existence for generations but now it is there even more than before in the current social media environment. The excrement will never be erased because too many like the smell of it and want it to remain (and even propagate it). That is how character assassination works/succeeds.