Since we can’t necessarily assume that you (or anyone else) would be able to get ahead of the train to flag it down, instead be prepared better for the next time (which hopefully won’t ever occur):
Find the WSOR emergency phone number on a nearby grade crossing, write it down on a card and keep in in your wallet or save it on your cell phone, etc. If that’s the number you called wiht no answer, then call the main number sometime and find out who to call instead. Be sure to tell them that, too, and give details - date & time.
Finally, I presume you noted the car’s reporting marks, car number, and about where it was in the train - maybe even which axle ? All of that would be useful to know.
Quick real-life story: About a year ago I saw a covered hopper go by a grade crossing on the NS Lehigh Line. The rear-most bottom outlet cover - about 6" diameter - was hanging down on its chain, swinging back and forth, banging on the rail underneath, and occasionally hitting against the nearest wheel. My concern was that if that cover had broken off and gone under that wheel, that might have been enough to derail the wheel. I called the NS 800-number, which I found out was the NS Police department, calmly and clearly gave my naem, expalined what I’d seen, gave them the car info (it was an FPAX = Formosa Plastics, I think), location - just the street name for the grade crossing on the Lehigh Line as I don’t know the nearest milepost (MP) or control point (CP) or anything else like that, direction of the train, and time. The guy who took the call was very courteous and professional, thanked me, and said they’d notify the train crew ASAP. Good deed for the day - done !
I now carry the numbers for the 6 major class I’s - BNSF, UP, CSX, NS, CN, and CP, as well as Amtrak and SEPTA (local transit agency) in my wallet.