Who in the government should I send my letter to?

I’ve never written to a senator or anything before, but now I have a very passionate letter about the ACA that I have written and want to send.

Who will listen to me but still has power to have any impact whatsoever on the survival of the ACA?

I plan to write to MA’s two senators. My county has 37 representatives in the house and that is a lot of letters unless I use email. I don’t have that many stamps, lol. I’m also considering the mayors of Boston and Cambridge, but I don’t know what they could do? MA has a smaller state version of the ACA (“Romneycare”) so it could be relevant.

What do you think?