Hello, I am Keith, one of the experts on Just Answer, and pleased to be able to help you with your question.
The item is not zero rated, but is exempt from VAT, a slightly different thing, but the effect on the customer is the same; there is no VAT charged on the item. Here is the relevant guidance from Equipment for the Physically Challenged:
'Goods qualify for VAT exemption if they are designed solely for use by a disable person. Some examples of qualifying products are as follows:
Not all goods sold in the UK have VAT added at the standard rate (20%). There are reduced rate [eg gas and electricity] and zero rated items also as well as goods which are exempt from VAT.
I regret that there is nothing that you can do in respect of this purchase as VAT has quite correctly not been charged.
I am so sorry to have to rain on your parade.
Thank you for your support.
Frankly, I do not think you have a leg to stand on. As I told you the item is exempt from VAT. Even if Amazon did misrepresent the price which I doubt, I would draw your attention to the following disclaimer in their terms and conditions viz:
'Despite our best efforts, a small number of the items in our catalogue may be mispriced. We will verify pricing when processing your order and before we take payment. If we have made a mistake and a product's correct price is higher than the price on the website, we may either contact you before dispatch to request whether you want to buy the product at the correct price or cancel your order. If a product's correct price is lower than our stated price, we will charge the lower amount and send you the product.'
Should there be some misunderstanding they would be entitled to the benefit of this wording.