Why has the camera on my iphone stopped working?

Tthe camera on my phone (iPhone 6S+) has stopped working. I thought it was due to lack of space (indeed, I couldn't even press the button and take a blank photo). That was for one side of the camera (they are two - selfie and the other side). (I had no space at that point, and nothing really I could do - installation of apps, etc.) I then cleared some space, and one of the sides cleared up, and I could take photos again. But that was for a short time, at some point it stopped working again, even though the space hasn't become close to 0. I read about it, and since then, have updated iOS, and even wiped the phone and restarted with a backup from iCloud. The camera is still not working. While it could be a hardware problem, I highly suspect that this is not the case, at least for the selfie side of the camera. How do I confirm it, and what is there left to try?