I was in the same boat, but for not nearly that same amount of money. After I talked to a lawyer I realized it was going to cost me more to recover the money so it wasn't worth it.
Libel - letter
Slander - spoken
Defamation - something else.
Libel needs to be written and published.
Slander needs to be said and broadcast.
And depending on who it's against, there are different levels of evidence needed. Like if you are a public figure, the person doing it needs to be doing it with the expressed purpose of injuring you name/actual malice.
Ages ago bud light was doing rock paper scissors tournaments for promotions one summer. I was at a bar one night and won. Went to regionals, and in the semi-final I was up against a guy that only threw rock. Each round leading up, every single throw was rock.
There is a bridge north east of town, that if you stop and turn off the car, your car won't start back up because a torso was found beneath it decades ago and the murder was never solved.
I was in the same boat, but for not nearly that same amount of money. After I talked to a lawyer I realized it was going to cost me more to recover the money so it wasn't worth it.