You need to go to the building supply and look at the following things:
- PVC "LB" conduit body
- PVC "LL" conduit body
- PVC 90 ell with 45 degree cap
These are the kinds of things you are up against. Once you see what they are, the trouble should become obvious.
Now, Code requires that wherever these things are, they must remain accessible forever without use of tools. That is what Code requires.
When turns need to be made in conduit without providing access, it's required to use broad curve pieces that allow feasible pulling. And there can only be four 90 degree turns between access points.
Now if these guys buried tees like this, or worse, used plumbing tees, then they violated Code two ways: them not remaining accessible for pulling, and, they would have had to assemble the conduit around the cable, by sliding piece after piece over the cable, a tactic which is never allowed.
And now, you know the reason for the Code.
So, you need to ferret out where these corner access points are, and put them to good use.
If it seems like they are not there, then you need to rehire these guys to pull the additional cable, and if they say it can't be done, get it in writing and go to the title insurance/home warranty/their insurer/lawyer. Because this was botched, they likely violated their permit/inspections, and the job needs to be re-done, at their expense. Concrete and all.