At the moment top level I've saw is 46, many players have heroes with 4* to 5* ratings, usually more than one hero if not their whole team. By this level having one 4* hero is an achievement. Please fix the problem as it's very obvious people are cheating by exploiting some unlimited gem bug, cleaning out merchant and refresh and repeat.
If you cannot find the source of the bug it's simple put a limited refresh times on merchant.