What would you do/think in this situation?

Almost certainly c or a variation among those lines.

They may not have one person in charge of keeping on top of submissions so it might just have slipped through the net. Or they get so many that keeping track is hard.

Don't get too disheartened. But open submission is a tough route

As someone who has been writing theatre for almost 30 years, I can tell you I've been in this situation more times than you can imagine. It's definitely nothing to do with the quality of what you've written.

I send stuff out all the time. 99 times out of 100 you hear nothing. Even when I've been invited to pitch a new show for a reputable theatre, and have gone along with actors to perform segments and talk about it, half the time you then end up hearing nothing back, neither positive or negative. You then contact said theatre and they apologise and tell you they're busy and that you will definitely hear... then still nothing. There's only so many times you can chase places!

I also know that it's nothing to do with the quality (or not) of the writing because I've had pieces that have done well when they've eventually been staged, but that have been ignored, or rejected, countless times before that point.

Biographies of famous writers tell me this happens to them all the time. Projects look like they're happening, only for the people keen on producing them to seemingly vanish. It frankly astonishes me that anything gets greenlit and makes it to full production, because there are so many hoops to jump through before that point, and no definitive way of doing that jumping.

Write because you love doing it. Write because you need to. Keep going. Sometimes you hear back a year later out of the blue. It's rare but it happens. But don't believe that, just because you've written something the best you can, that you've done your bit and the rest of the process will follow neatly on from there. It's totally random. It's luck. But that luck can only happen if you keep trying, over and over again. It can take years. It drives me crazy, but I keep having ideas that I want to pursue, so I keep diving back into the craziness. On the few occasions it has worked out, it's the best feeling in the world.

Good luck!!

Rude is rude. If they can’t even acknowledge receipt then call them and ask. Not pushy, sensible. We don’t want the NT staging your masterpiece at the same time as the RSC do we? Good luck with all these submissions. By golly we need new voices.