Sorry about the situation
It disturbs me to read so many people having issues with home and landscaping projects in this area.
Make sure you report them to the BBB and you might call senior crime board. Does sound like she did try to rectify the situation but she should be the one going head on with the paver company not you and got new pavers elsewhere, finished your project and dealt with, but sounds like they're not going to help you any further. Hopefully someone here might be able to direct you to someone or a way to make them look right
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I would almost call a company like Lowes and see if they can come out and see if there is a way to fix it. I know its more money down the drain but they do stand behind there contractors work. We've had issues with a contractor and they sent someone out right away, brought in a different contractor made sure everything was rectified to our satisfaction. If the stain is sealed in not really sure what can be done though
Wish you good luck and hope you're able to get it fixed.