If something has gone wrong then your best bet would be to contact eBay Customer Service using the following link https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid. When the next screen loads up scroll right down to the bottom of the page and click on the blue button to request a call from an eBay representative. Explain clearly and in full what has gone wrong - I had a similar case myself not too long ago and the eBay representative was really helpful, looking into the case very closely and then opening an additional two cases on my behalf. To cut a long story short, the seller continued to mess me around for a bit, but refunded me in full the day before I would have been able to escalate both cases to eBay in order to get them to force a refund, so asking eBay to step in and help proved to be worthwhile in my case.
If you purchased three separate items and paid in one go by placing all of the items in your basket prior to making payment then open a case for each separate item, escalating on day four if necessary. If, however, this does not appear to be possible then contact eBay Customer Services using the link I provided above. The lines are open from 8:00am to 10:00pm from Monday to Friday and from 9:00am to 6:00pm on Saturdays and Sundays. However, the best option is to call first thing in the morning when the lines open, as that way you've got more chance of getting a call from an eBay representative in Dublin, as opposed to receiving a call from an eBay representative working out of eBay's Philippines-based call centre if you were to leave it until later in the day.
Should eBay fail to help you with this matter then your next course of action would be to open a PayPal case if that is how you paid for the items, so long as it has been less than thirty days from the date of purchase. PayPal tend to look into cases for more closely than eBay do, so when they realise that the items never turned up they'll more than likely issue you with a refund. However, if you do go down this route then make sure that you escalate the case before PayPal's twenty day cut-off date should you need to escalate the matter in order to receive a full refund.
In the event that you didn't pay with PayPal and paid with a credit or debit card then your next course of action would be to contact your card issuer and start a chargeback. You have a hundred and twenty days during which to do this, although if you do end up going down this route then you should stand a decent chance of receiving a total refund of the money that you paid to the seller.
