Shingles placed with no decking board underneath

We just had our roof replaced. We had a lot of water damage and rotten decking boards that had to be replaced. We were not happy with our attic ventilation system, so we asked the roofing company to install ridge vents. We have a section of our house were a shingled roof meets a flat roof. We asked if a ridge vent could be placed there, and after consulting with his boss, the roofing manager told us yes. The roofing company completed the job, but my fiance found multiple mistakes, such as no flashing, rotten decking boards that were not replaced, rotten fascia that we had asked to be replaced, decking board nails completely missing the rafters and/or splitting the rafters b/c the nails were too close to the edge, and the list goes on. They agreed to come fix our list of problems, and when they returned, they decided that section of the roof couldn’t have a ridge vent, so they removed the ridge vent and placed shingles over the area. My fiance has discovered that they did not fix the decking board where there is a ‘space’ to allow for the ridge vent and just placed shingles over the area where the ridge vent was. He was only able to see this because of a hole they accidentally made in the ceiling when they dropped a tool thru the ceiling. We both feel like over time these shingles that are not supported with decking board are going to sag and leak?? We also still have rotten decking board that didn’t get replaced the 2nd time, even more decking board that is not nailed into the rafters, and some other issues. Basically, despite our due diligence and the 4.9 star rating they have, we ended up hiring an incompetent roofing company, but I just want to know what is going to happen to the part of the roof where they just shingled over where they removed the ridge vent without putting wood underneath the shingles-there’s no roofing paper either, my fiance can look up and see the shingles.

Don’t pay them and hire a competant contractor with a written contract and make sure they do it correctly before you pay them