Returned item not recieved from buyer. What do i do next?

[Tortoise]

Buyer complained new without tags children's clothing item has a stain and must have been worn.

Offered refund upon return on item.
Buyer says sent on 11th Aug. Item hasn't arrived yet.

What do i do about it? Buyer not happy! Assume not sent recorded as they have receipt for postage but no mention of tracking number.

explain that you can not refund until you have received it. keep it calm and polite. They may open a dispute but without tracking number that proves you have received it back they will not win the dispute

Thanks, have said that and also that i will check at the post office as i have been away (My Brother was here but might not have heard post).