I would question it no doubt but it might turn into a fair bit of back and forth followed by a falling out. In 30 years I've never got it that wrong on an invoice and I'd be keen to hear the excuse.
In case they've already done the job as your post doesn't make it clear. Is it possible they chose to level the walls with tile adhesive and ended up using a huge amount because the walls were really pissed?
Yeah thats as good point, the walls could be a shambles and he'll need a ton more than what you work out going by the sizes. Anytime we've done tiling we've always resheeted the walls to sort this is issue out.
I would question it no doubt but it might turn into a fair bit of back and forth followed by a falling out. In 30 years I've never got it that wrong on an invoice and I'd be keen to hear the excuse.
In case they've already done the job as your post doesn't make it clear. Is it possible they chose to level the walls with tile adhesive and ended up using a huge amount because the walls were really pissed?