Hello. This exact same thing happened to me. Also a mobile phone. The buyer sent me a message stating that they had received a package with a wire and a link sync modular????? I called eBay as never bother with the message system.always speak to someone and ask their name at the start of the call. I was advised incorrectly at first as they suggested the buyer start a return so I paid for a label to have an empty box sent back. They should have advised that when the buyer raised a dispute the reasoning should have been item damaged or tampered with in transit. Anyway a long story short, they also tried to tell me that I could not get my money back but after I gave them the names, dates and times of everyone I had spoke to on eBay and requested all the calls to be listened too they advised I was given incorrect information and I was covered as this happened in transit. 
when you take your items to be posted demand they weigh the package and obtain a paper receipt .you also do not have to use the simple delivery you could void that label and send your own easy, if I send anything of value I always make sure to not use the simple delivery label( if customers pay post the original label cost will go back to them but if you pay post you will have to fill in a ‘simple delivery refund request form) you can find this in the help section. Always send expensive like a couple of hundred or over with Royal Mail special delivery. This has to be signed for when changes hands anytime during in transit and cannot be delivered with out signature. If sending a mobile phone always take note of the imei number then you could have called the police reported as stolen in transit and they can black the imei number leaving the phone useless as soon as connected to any network it will be blocked.

if you suspect the customer of being fraudulent then tell them you are going to do this, if they have the phone they will cancel the request to return.

i don’t know if the experience you have had with the phone can be resolved but in future follow what I have said and you will be ok. If ever in doubt always speak to an actual person and record everything I.e names, dates , time, brief description of call and all paper receipts and most importantly if a mobile the imei number so you can block the phone.