At this stage there is not much to be done with ebay and Paypal because they have ended their involve,ent and they follow very rigid procedures which will not overturn the outcome. So your rights are very much against the buyer directly and you will have to pursue them personally if you wanted to go any further with this.
What you have to consider is that whilst you can contact them and ask for payment, if they refuse then the only way to try and get anything back is to go to the small claims court. For a value of £7, that may not be the best idea as the fees will easily overtake anything you can get back from this. Also there is the time and effort involved in claiming, plus the fact there is no guarantee you will get anything back.
But it is an option (albeit the only one) and it is there if you really felt like you had to take this further.
You can find details on how to initiate a claim here:
I suggest contacting the buyer initially and threatening legal action if they do not resolve this directly with you, just to give them a chance to do so, but if they do not then at least you know where to go next if needed.
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