“See the Cherem which says so specifically”
You cannot possibly be telling the truth, because the original text of the cherem does not exist. Nobody for centuries has known exactly what it said, which is why there’s the machlokes rishonim over whether it expired in the year 5000. The Shulchon Oruch says it did, but many others say no, there was never any such expiration date. (I’ve even heard a modern amhorzatzus that it expired recently and the Israeli Rabbanut renewed it, as if it would have the authority to do such a thing.)