Handling inappropriate behavior

[hill8a]

We are sellers located in the USA, sold an items in the UK. The buyer complained of slow delivery with profanity and bad attitude.

After few message exchanges trying to help him to track his package in the UK Postal service he toned down his messages.

Today he received his package and requested to refund total or partially the custom fees which he should know they might apply with international purchases.

When denied the refund (we reviewed his feedback, seems that he ofter request refunds) he answered "well its negative feedback them im afraid its up to you if you going to be a tight

let me know"

What should we do?