Wall mount tv

I've an external wall with around 20mil of plasterboard then 30mil of space to the brick work. I've used hollow anchors although they won't lock into place they just keep turning exposing a bigger hole. I've then tried Anchors with an aim to drill into the masonry but they won't lock and tighten. I've used all the correct diameters but don't understand what I'm doing wrong. Could anyone please help as my arms are attached to the TV just need to mount the bracket to the wall.