Employers have to make adequate arrangements for someone if they have a disability at work. If they refuse to do so, they are not complying with the Equality Act and can be prosecuted for it. You can do one of the three options, you can; talk them informally first to see if they even realised what was going on. You could complete a written grievance or make a complaint. Or you could make a claim to the employment tribunal. You should always try to sort things out with your employer before seeking external help.