I sell new iPhones, which I import from China based on demand alongside other items.

On 2nd June, a customer reached out to me that she wants to buy an iPhone 12 promax 256gb and 512gb.
I told her, "Let me check out availability from my supplier." I reached out to my supplier and confirmed that 256gb is available, but 512gb is not available. Then I reverted back, telling her that 256gb is available.
She asked if it's a new phone or fairly used, I told her plainly, "New phone but open box, and it comes with accessories."
Then she requested for powerbank, phone cooler, and pouch. I told her that powerbanks are not shipping through flight only through sea, and it takes 2 months to arrive. But the phone, phone cooler, and pouch is being shipped through flight and takes 2 weeks.
She said ok and then paid for the iPhone 12 promax 256, phone cooler and pouch..
407k for the iPhone, which includes air flight shipping fees. Should I have included the waybill, but instead of 25k, the previous fee I do pay for iPhone shipping and clearance, the fee was increased to 35k. So I told her the fee no longer includes the waybill cos of increased price, so she will either come and pick up or it will be dispatched to her. She said okay.
Less than 2 weeks later, the logistics company reached out to me that my items have arrived .Aside from her phone and other items she bought, I had other things I imported for my customers.
I told her, "Your items have arrived, and this is the fee for shipping the phone cooler and pouch. She made payment for the shipping of those items.
My friend who always goes to the airport to receive and pick up my items went and got the stuff, then noticed that the iPhone 12 promax wasn't among. I reverted back and told her that her iPhone hadn't arrived, as it takes 2 weeks to. On the Friday of the next week, which made it exactly 2 weeks, I got another message that my items have arrived.
My friend quickly moved to pick it up for me. She's always the one because she stays not so far from the airport, unlike me that lives much far..
Arriving, before u sign that you've received your item, you check your goods. She checked my goods and noticed that it was iPhone 12 promax 128gb that the supplier sent instead of 256gb. There and then, she signed for a return of the goods, and it was given back to the logistics to send it back to China..
The supplier was contacted, and I asked him why 126gb was sent instead of 256gb. He said 256gb price has increased, and the balance will be sent since it's 128gb that was sent to me. I told him it had been returned already.
Asked, how much increase, he said 200rmb, I got back to my customer and told her that this is what happened with the iPhone that was sent to me. The price has increased. Can you pay an extra 40k to get the 256, or do you need a refund? "She said, refund. Then I told my supplier but he insisted there was no refund.
This is actually the first time I'm requesting a refund on an item, but he said it's already documented in the iPhone store and transaction processed. So he can only send 256gb and not refund.
She insisted on a refund. I told her what happens is that I will receive the phone when I sell it here in Nigeria, and then I will refund. I have already incured losses sending back this phone when the wrong one was sent and will still pay for it to be shipped back to Nigeria. "Over 60k already". After much back and front, out of the 40k plus, I told her to pay 20k, and then I will balance up. Despite I have already made losses but I just want to satisfy my customer at the end of the day. She later agreed and paid.
The phone was shipped, in a week time, it arrived cos I had to use air express which is costlier but takes 1 week instead of air cargo that takes 2 weeks.
I told her that it had arrived. She requested a picture of it, and then I sent her a video of the phone..
Kindly check comment section for continuation.