I got one a few months back because BNY Mellon is the transfer agent for some JP Morgan restricted stock that I own...however, mine correctly identified the company I used to work for and had the correct account cross-reference number on it. When I called to verify, it was legit (I called the transfer agent directly, not the customer service number on the letter)...so now I'm into my 4th month of Experian monitoring...I get a nice email from them every month indicating no changes in any of the 3 credit agencies. I also put a hold/stop on my credit files for the first 3 months (so yeah, no duh...of course there wasn't any changes!)...
Yours sounds scammy to me...if you call and are asked for your SSN, request they use other information to confirm who they are speaking with. Also, call BNY Mellon directly, not whoever sent the letter.
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1000 Billions = 1 Trillion