But the general population votes on who will be in congress right?

Edit: so if I vote for John Smith and then I find out he voted against this healthcare issue I care about; I will for sure not vote for him again, instead for a candidate that keeps their promises.

At least that’s how it works in my country, all the votes in congress are public, you can even listen in to most of their sittings.

If both of the major parties are against something, you can only vote for some independent third party, which in the foreseeable future will never even have a single seat in Congress (not to mention a ruling majority). In countries without winner-takes-all electoral system (everybody except UK and USA) it's much easier for smaller countries to gain ground and hence they have a wider selection of viable parties, but in the UK and USA people are pretty much screwed.