I know of many Christian Leaders who have told him to cease and desist.
The first are the Elders of the Church that stripped Harold Camping of his teaching ministry — The Alameda Community Church.
Dr. James White of Alpha and Omega Ministries has called out camping almost every month. He even debated Camping publicly on this. See here :
Hank Hanegraaf of the Christian Research Institute and The Bible Answer Man has been telling me to stop since as far as I can remember.
Greg Koukl of Stand to Reason Ministries have done the same in his radio program.
These are the first people who I can think of.
The Alliance of Confessing Evangelicals, have refuted Harold Camping for years. See here for example :
R.C. Sproul Jr of Ligonier Ministries has called Harold Camping a false prophet writing a series of articles on this. See here :
I’m sure one can find MANY OTHERS.
The problem with Harold Camping is not that there are no Christian Leaders who have asked him to stop this prediction business. His problem is HE STUBBORNLY REFUSES TO LISTEN!!