Buyer hasn't returned item that was mistakenly sent

[heidisseekandfind]

On April 18th I sold two items to two different customers, customer #1 and customer #2.

Since I was out of town, I had my helper send both packages out. Long story short, each customer received the wrong item.

Customer #1 returned item to me, great communication etc. 

Customer #2 was upset, I sent a prepaid postage bag for them to send item back to me, with lots of coaxing and communication on my end, they agreed.

 Meanwhile, I sent the correct item to them, but still haven't received the item back, nor have they responded to my requests for communication, and customer #1 is tired of waiting and has requested an immediate refund.

I've fully refunded customer #1, and offered the item at half price when I finally receive it from customer #2.

I have 2 questions: 1.) When should I involve eBay help? 2.) Should I expect a resolution in my favor, since the mistake was originally mine? Any feedback is appreciated. Btw, the item #2 still has a value just under $50.