New flat roof leaks. Returned 3 times. Should it be replaced?

it is possible to make mistakes fitting any roof system but the fact it hasnt been solved after 3 visits sounds like its been fitted incorrectly, a flat roof system usually consists of a black underlay and a green mineral finish top sheet and the fact the water is getting through both layers to leak into roof means a top sheet of debotec will just be like painting over the cracks in a wall in my opinion

This roof has been laid incorrectly, you should get a nailed layer of sbs underlay which allows for movement of building then another layer of underlay torched on top which is your main water proofing layer then a mineral finish with perimeter being flashed up. all roofs should carry a 10 year or 15 year guarantee. Do not let this roofer put a layer over the top as this will not be correct procedure. Regards Aaron