I think a good solution would be they give you the goods. You paid for them and have proof of purchase. They're yours.
I don't believe they're entitled to any payment for work completed as its seriously below par to the point of being dangerous.
If i were you id write off the cost of tiles you've paid against anything they ask in labour.
Put an ad on the looking for a Tiler board on this forum and perhaps visit the plumbers forum as well. Check a few references a get good professionals in.
Least you checked their work and there's no harm or damage done. Just out of pocket on the tiles.
Shame you're not a little closer id come quote you to do a proper job.
Thanks for all your advice, will see what happens on Monday, I have my Dad as back up as not sure they would take much notice of woman, will update you all on Monday, wish me luck!