Why are JW's so insistant that you HAVE to use the name Jehovah?

In Hebrew the name of the Lord is written in all consenants without vowels because the Hebrews were afraid of reading the name of God and being killed because it was so holy, therefore they never fully wrote it. So there can actually be two names for God when looking at those consenants in the original languages which is Jehovah or Yaweh, nobody is sure which is correct. So to say that you're certain it's Jehovah is not 100% true or factual, however i saw a bunch of the leaders of JW claim that they knew Hebrew and then when they showed them a Hebrew alphabet they didn't know any of it when they claimed they did. This brings to question their credibility at all. Plus last i checked in the Bible, you can pray to Jesus who IS God (not some archangel Michael like a lot of JWs teach). So since Jesus died for our sins and through Him we're saved, it makes a lot more sense to pray to Him than put so much emphasis on a name that no one is positive of.