I doubt there can be any reliable statistics since most operate in the open and people don't believe they are cults, and some work more covertly and are only exposed when something happens to bring attention to them.
the statistic that was showed on TV was these people got caught. And the number of complaints are growing, Some are being investigated by the goverment. Some of them are interviewed by the press as to why people left their churches.
Some left their churches because of abuse, so they start their own cell group, home churches. Form there some of the abuse arise too. Some turn out good.
I forgot the name of the woman who is an expert in cult watchers. The goverment consult her time and to time.
She talks about the symptoms of a cult. Which is pretty accurate. Mind control, giving up decision making slowly and giving it to the leaders etc. She is around 65 years old I think and has been around for a while watching it grow. I saw the show a few months ago.