Lowe's

I purchased 3 toilets, recommended parts, basic installation, and extra installation for shut-off valve. 3 years later the shut-off valve failed causing massive damage. I have my original receipt. I have a time stamped picture of the toilet one hour after failure with the old part, the emergency plumber has it in his notes that the old part caused the failure, the Lowes contracted plumber denied my claim because Lowes did not hire him to install new parts so he did not install new parts, and Lowes denial because per them I can't prove the new parts were not installed. The denial letter from their plumber says they did not install new parts. I asked them what I was missing? I am 70 years old. They asked me why I didn't compare the parts list to what was installed. I trusted Lowes but that was a mistake. They took my money but didn't do what they contracted for. This leak caused massive damage. I have all the evidence plus witnesses. I am not responsible for mediating the plumber and Lowes.