Blocked shower drain, it empties but always returns?

I have a blocked shower drain. It fills up the tray straight away, but when I plunge it runs away at a rate of about 50%. The problem is that this is one of those modern shower drains with a little plastic sleeve/basket which is supposed to catch hair, you can lift the sleeve out but there is no hole that leads to the exit pipe so you cannot use any of the snake tools to clean the pipe or even a camera to see what’s going on because the water exits the drain by rising in the recess behind the sleeved section and then running out of the pipe. I have a heavy-duty pump plunger for sucking water back up and then blowing it down under pressure. I have also tried a powerful wet vacuum to suck out the water hoping to drag what ever is blocking with it. I have also tried chemicals but they were useless as always. I cannot really contemplate tearing up my heavy cemented in shower tray! Please can someone offer advice?