The Titanium number is 1 (800) 399-4229. Published here: https://help.marriott.com/s/article/Article-22353
Same article for Platinum, phone number above: https://help.marriott.com/s/article/Article-22352
Here's the Ambassador article but no published phone: https://help.marriott.com/s/article/Article-22355

"Dedicated Elite Support" is only for Platinum+, general phone number is 1 (800) 535-4028.