Poor service and quality

We did a canvas of a family photo and was a complete disaster. Firstly the quality of the canvas was so poor that it was falling apart in the shop. The image on the canvas was full of flakes and we were told it was n poor quality photo that was supp****, but what I don't understand is that we did 3 canvases previously at them and it was only a 16 Megapixel and the photo that was supp**** for this canvas that was a poor quality picture is a 48 Megapixels. I would like to know why they didn't print it in front of us like the previous ones. I would like an answer from them because this really poor service that you pay so much money for a thing that is falling apart in the shop, then they run to the back at the shop to try and fix it