Ouch - Wouldn't sleep at night if I turned out work like this, really feel for you. Agree with previous posts that setting out was way off the mark and needs starting again.
From experience in my previous career I would suggest a firm, but very calm and assertive approach indicating the faults and what you expect from the job.
Get the plumber and electrician on site together - point out it's their reputation at stake, and the Electrician - if he's worth his salt should stick up for you based on his recommendation that the plumber could 'tile'. My line would be that you'll pay the bill only if they get a pro tiler in to sort the job out. If all else fails and they don't play ball then a gentle suggestion of small claims court to cover all costs should do the trick....Good Luck