Scope of work change, contractor not changing price

[Mike Johnson]

I live in a 100 year old house and had some sagging floors due to the main beam in the house shifting over its life. Called in a basement company who specializes in this work and they draw up a proposal to install a parallel steel beam in the house, couple up 15 or so floor joists and add and install 3 adjustable jacks to support the new beam in the house. The new beam was actually going to be in the center of the house because the original support was a 1ft+ not in the center. I agree to the scope and proposal and the price of $5600.

So the crew comes out to work, and the lead said the plans do not make any sense. They basically scrap the original proposal and verbally said it was impossible to do because he would need to replace all the floor joists in the house and any lolly columns supporting the house would be useless. We agree to change the plans (to be honest they said i didnt have much of a choice) and the new plan was to add the 3 adjustable jacks to the original main beam in the house and add support by bolting in a few 2 x 6's onto the original beam so the jacks can be supported.

So the work is complete, id say the floors in the house improve 50%. The new scope of work doesnt have a new beam, or any floor joists and I feel was significantly less work than what was proposed and therfore less than $5,600. In my discussion post work the sales guy is trying to say it was less work however since they worked on the main beam it should be more money because of liabilty reasons but is not increasing his price. I want to get some thoughts on what I should do? I paid 50% already and am holding the other 50% currently.