To get a refund using the Money Back Guarantee, you do have to follow the Ebay process.
Start a return case through Ebay.
Seller has 3 days to provide a label.
Then if the label is not suitable, you have to contact Ebay and they will ensure a correct label is sent.
Once tracking shows the item has been received by the seller, the seller has 48 hours to refund you.
If they don't, you go back to the case and ask Ebay to step in.
If you are not proactive and you let things slide, cases can close in favour of the seller. It looks as if you contacted a slow and unhelpful seller rather than asking Ebay to step in sooner.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)