Help please with a odd mix-up

[nicjam_123_123]

I was wondering if anyone could help with a problem I sent a item on the 13th of January using a generated qr code. Then the next day I posted another item but somehow it's generated the same qr code and ive not found out until the second buyer has said they didn't receive the item. On looking at both postage receipts ive noticed the same tracking information. What can I do now please 

[jckl1957]

Contact 'buyer A' who should have received two items.  Explain one item was sent in error and ask them to return it to you.

They won't be able to do this through Ebay/a return case because it's an item they didn't buy.

You will have to pay for the return.  You can send them a payment via Paypal or direct to their bank or possibly send them a stamped, addressed postage bag/padded envelope etc. for them to use to send it back to you.

You are in the buyer's hands so be really apologetic and helpful in enabling them to send the item back.

Has 'buyer B' opened a case?

if they have you can refund them in full or ask them to wait for a few days while you try to get their item back.