been fitted about a month
Having been a member for almost 20 years I imagine you know that the time limit for eBay'smoney back guarantee is 30 days from the date of delivery.
If it's less than 30 days, open a case while you still can. If it's beyond 30 days eBay will have no further interest. Your payment provider e.g. pay of your credit or debit card issuer may be able to help.