Marriott has a few employees that monitor and help FTers with issues. Their FT handles are "Marriott Bonvoy Lurker", "Marriott Bonvoy Lurker II" and "Marriott Bonvoy Lurker III". You can send them a PM (Private Message) with your information and problem. Depending on the issue, they can help you understand why the issue occurred and fix it (if possible.) And if needed, they can point you to the correct department within Marriott that can help.

But as some have already mentioned, based on the information you have provided so far, it doesn't look like you met the normal requirements for LTP before the merger. Your stated number of nights isn't enough and $$$ spend isn't a part of the LT status requirements. So most likely if you did have LTP status, then it must have been through something other than the normal means (i.e. original members were given complementary LTP status 10 years or so ago, something else?) If you reach out to one of the Lurkers, they might be able to help you figure out what happened and if you really should have LTT or LTP status, they can probably help get your account fixed.