Sounds like chicken and egg situation here. Shopee want you to return first before give refund. You want refund first only can send back item

Once I ordered an iron and there was ironing board FOC. Somehow I received 2 ironing board instead.

Contact seller and the investigation showed that they mistakenly sent 2 iron to another customer buying same iron. So, I just need to go to nearby JnT for free return of one of the ironing board. After several days I called seller when I should expect my iron. The seller told me that they have yet to receive the iron from another customer. Seems like the customer location is quite rural thus take longer to return.

This means even if it was the seller problem, it became my accountability to bear the inconvenience. The shop can just send me another one from the shop and just need re-stock the one returned by the other customer. Poor customer service relationship

That's why I said poor customer relation service.

Only two reason I can think of:
1) They are lazy to change record which serial number has been sold in system
2) Their system not allowed to alter data on good has been sold.

Forgot the shop name but has good review. My feeling is that this shop is not home based but has well known quite big retail store.