Wondering if there is anyone out there with a decent understand of GDPR in relation to my query.
Basically I have a stand alone online retail shop and an accompanying Ebay shop. I do quite well through these businesses, but I am basically a sole trader, so not mega turnover.
Via Ebay platform I sold an order and sent it out to customer (A). Unfortunately I had accidently enclosed another customer (B's) order with customer (A's) - it was in a sealed envelope addressed to customer (B). Hope I have explained that well 
I'm not sure how I managed this feat, but hey I'm human and occasionally make mistakes.
Lovely customer (A) contacts me to tell me what I have done and offers to forward the order on. I reimburse customer (A's) postage and contact customer (B) to explain situation and she's seems happy enough with arrangement.
Few days later customer (B) contacts me to inform me that I have breeched GDPR laws, how dare I share her information with a stranger and that she wants full refund etc.. 99% of my customers are lovely, so this one has thrown me a bit.
The order is on its way to customer B and is of quite high value and in as much as I can appreciate Customer b's concerns, I can see this as being no different to a postman delivering an envelope to the wrong address and the recipient forwarding it on to the correct addressee. So I am loathe to just refund.
When I have tried to look up online the guidelines it saying that I need to report any GDPR breeches to the data controller and I can't find much information on this kind of scenario.
Can anyone have any experience of something similar, or good knowledge of GDPR regs?