This kind of thing that has changed over time and has not been caught red-handed is also difficult for the police to deal with. It is difficult to arrest people and it is impossible to file a case.
If you really want to solve it, the only way is through judicial channels. You must extract the evidence first. For example, telephone recording or meeting recording, or looking for other victims, but the probability of success is very small, plus the cost of litigation and evidence collection. If the lawsuit fails, the loss will be even heavier.
Although it is not to let criminals get away with it, sometimes we can only take a step back.