new bathroom problems

It sounds to me like the vinyl needs to be taken up and the boarding fixed down again using a different method.
There are different thicknesses of vinyl also which is a consideration and the company may say it is too thin.
Also the taken up vinyl made not be re-fitted successfully.
You need to talk it thru with the company but they have a responsibility to you as a customer to make the fitting suitable for purpose and clearly it is not.
I would ask to speak to one of the managers.

Thank you all for your response. It helps to have another opinion. I'm going to contact the store again as they employed the fitter.

If he's stapled the boards down no amount of banging them back in will stop them from working their way back out, he should have used pins with rings around which grip better and won't work their way back out again. They are called annular ring shank nails but he should know that.

Agree with B9 he must take up the whole lot and redo it, if his stapler wasn't working correctly. It's down to him to do the job you paid him for properly.
I would imagine the boards cannot be attached correctly, if he is just tapping staples down they are not hooked in as they should be. You may have problems in the future if board are able to come loose.

I would email the shop, so you can be assured that they received it, with a fairly business like letter, telling them that as the floor is proving to be not fit for purpose you would like them to remedy the matter at their earliest convenience.

I would call him back, point out that the flooring is not fit for purpose, since it is damaging your feet, and that obviously it is a problem with the way the floor has been laid. Ask for him to take it up and do it properly, or pay you for someone else to fit new flooring.

Where did you find your fitter, if through a shop or organisation, you can go back to them. If not, point out that you would like to leave a good review for him, but that unless the flooring is permanently sorted, you will have to leave an unsatisfactory one and warn people in the neighbourhood!

Yes I've paid I'm afraid - well everything looked fine. I only became aware of this problem when I stepped on a sharp point later.

Have you paid the bill yet? If not don't and contact the firm before the date the bill is due on, explain your dilemma and request them to either relay the floor entirely, or to pay for new vinyl, so you can get another firm to lay the floor properly.