I'm not sure what the buyer wants

I'm a new seller that listed a vintage camera lens. I wasn't able to get it to the post office as fast as I normally would because I was sick. It was purchased on Saturday and I wasn't able to get it there until Tuesday.

The buyer messaged me on Monday asking when it would ship. I explained everything and apologized. The post office seems to be really backed up because the tracking is not updating. It was supposed to update yesterday and it didn't, so I called and they told me it would update today and it didn't again. The buyer is angry and blaming me for the issue. I apologized and told them if they are no longer interested in the item they can send it back for a full refund even though on the listing, it said no refunds. They later calmed down and said they were just disappointed because it was for a gift.

What should I do in this situation? I admit I was upset (although I stayed calm with the buyer) because this buyer got the lens for a very low price. I gave them the option to return it for a full refund but they are continuing messaging me, not with what action they would like to move forward with, but explaining they are disappointed. What is the right thing to say in this situation?