Last leg DHD there is no FDP limit. Am I wrong?

14 hour contractual limit.

see above
cant be scheduled for more than 14 hrs of duty

I was told by CS that last leg dhd doesn't count as duty.

So are you saying you accepted more than 14 hours with no extension?

Or 16 hours from beginning of RAP

There's a difference between duty time and flight duty time. Deadhead is always duty time, and is flight duty time if it is in the beginning or middle of your flying day, just not at the end.

for 117 FDP limits it doesnt
per our contract it does. You cannot be scheduled for more than 14 hrs of duty

Wow I just spit my Dr. Pepper through my nose. Lol. I’m not sure what’s worst quoting CS in a contractual argument or needed CS to tell you that a DH doesn’t count as duty.

Simple test to determine if you are on or off duty. Do you have to wear the uniform? Can you drink?
Answer those questions and you have your answer.