No excuses for such a bad job, for the price you are paying this is absolutely insulting, I wouldn't even get any cowboys to do such like workmanship even for free, as it would bugger up my expensive tiles.
Just tell them to do it right or if they can't then leave, as they will end up ruining your material. Don't accept any excuses if they say your walls are not straight, it is their job to do it right, don't pay them anything, if they get stroppy or threatening you can always call the police.
I bet they are unskilled migrants claiming to be experts, but most of them have no skills, we get plenty of them around London hanging outside
Wickes and B&Q store car parks, looking for day jobs, and worst of all they even got the cheek to state their terms, like I charge £x per day, and will take two breaks 1/2 hr each, and without some cans of beer in their hand they can't move, yes I can do tiling, no problem etc etc, they never declare their income, don't pay taxes, and their work is atrocious, for that price you are paying, you would have got proper UK trained and experienced bathroom fitters and tilers.
Please don't tell me they are UK bread builders!
A mate of mine is having his bathroom refitted with new floor and wall tiles, taking the bath tub out and instead having a shower fitted, new pan, new sink, all for A GRAND for labour, and \i have already seen the work, its a lot better than yours!