Dispute with the seller over the wrong items sent

[Puwanit]

I have order 3 transparent melting popsicle sculpture in pink, rainbow, and blue. I did order on 21 /04/21 and they were arrived on 14/06/21 , 7 weeks. But the point is they are not the colour that I ordered . They were all in blue colour. I raised this issue to the seller  but the answer is  that they sent me the right order.  Obviously, the seller did not want to take any responsibility at all. So I open the case with PayPal  asking for partial refund of $20.00.  PayPal send me the email said the the seller agree for full refund  but I will have to return the items. 
my question is that who will be responsible for the shipping cost? And if I have to pay for it , I do not think it   Resolve anything in my favour . It is clearly the seller fault and I have to be responsible for that mistake . It is like  forcing me to accept them . 
and what happen !  , if I send them back to the seller in China  and they said they don’t receive . 
anybody please advice 

[kernowlass]

@Puwanit 

In the event of a dispute you choose your seller and not Paypal so you need to bear in mind possible return trackable costs before you go ahead and buy from that seller / country.

Paypal state this >>
IMPORTANT: You may be required to return the item to the seller or other party we specify as part of the settlement of your claim. PayPal Buyer Protection does not entitle you to reimbursement for the return shipping costs that you may incur.

Although they will compensate you for some of the cost if you have activated this at some point before you made that transaction.
https://www.paypal.com/us/smarthelp/article/FAQ3544

You also have the option to do a chargeback via your card issuer instead of a Paypal dispute if you funded your Paypal payment via a credit card.