You need to keep riding everyone until they let you in. Most contractors don't want the client in the building because most clients have zero clue what a building under construction looks like.
Personally I think everyone who is buying new construction or a renovation should go and make sure the unit they are purchasing is not only built correctly but to see what they will be living with for a long time. Developers and builders for the most part take the we'll construct it and you can inspect it when you can't see what is behind the walls.
I had it worked into my contract that I was allowed to bring in my own inspectors at certain milestones in the construction. The builder hated it, but he really had no choice as the developer agreed to it to sell my unit to me. I caught defects that were minor to fix when I caught them but would have been annoying later on. Examples you ask?
There were other little things like poorly routed electrical wiring, but those were not out of code, just not how I would have done it.
- Cable wire cut 15 feet from outlet and duck taped together.
- Bedroom wall out of level and plumb. The real estate agent told me that the drywall would fix it. Fortunately I actually work in construction and knew to ask for it to be corrected.
- The concrete floor had a slight depression about 2'x2' it simply needed levelastic but when the 'exotic hardwood' floor went over it, man would that have been an annoying squeak.
- The toilet flange was broken. The toilet would have rocked. I would hope the finish plumber would have noticed before I did, but it was a simple defect.
If you didn't ask for the right to inspect and visit in your contract you're pretty much relying on the good will of the developer, builder and real estate agent. I might suggest if you get no where, have your lawyer write a note officially asking for the right to inspect the unit as soon as humanly possible.
It's your money, why not ask those building it for you to show you thier work. If someone doesn't want to show me the work in progress, I question the quality of the work. Professionals are expected to work in a workmanlike manner. In reality, cutting corners just makes the world a crappy place.