Terrible service

I purchased a product, but when received there was an item missing in the box. I raised the issue with them and attached photos that they have requested. I followed telephonically up again with them just to be told they never received the email. I have proof that the email was sent and gone through. It appears they are not eager to address my issue and thought I shall just forget about it. I paid full price for an incomplete set of items. The item missing is a crucial piece of equipment.