Unfortunately I've faced poor support from the Samsung Online Shop Team too when I had to send back a Note 20 Ultra 5G Exynos version as it too had signal and connection issues.
I also sent back the free Samsung Buds Live earphones, and I sent back the Samsung Leather Back Case as that has been discounted due to the sale of the phone.
Samsung arranged for DpD to collect it all but on Samsung receiving the parcel the refund didn't happen for the phone.
They did refund the free Samsung Buds Live for £0.00
After numerous emails and phone calls it appears they couldn't find the Samsung case so we're withholding over £1,200.00 for the sake of a £35.00 case !
I asked them to refund the phone and continue their investigation of the case but that didn't happen either.
I ended up having to find the official Samsung online page to email the UK CEO directly to get a resolution.
When an item has been given for free then if a person is returning the main item then the freebie has to be returned too.
You may find they won't refund the money until that has been returned.
In regards to the trade in of a phone they'll look at your personal assessment of the phone, and then assess it themselves when it's received, which can occasionally mean the original offer can be amended as their assessment differs from yours. I would assume they'd contact the owner to advise and give the option to go ahead or have the phone returned to them. I'm not sure as I won't use that type of trade in option.
This is why I either trade my phone's into my local Samsung Experience Store.
Or sell them privately, not to auction sites such as ebay, and I usually get a better return in amount that way.
If a phone has been returned and meets the conditions and criteria then Samsung has to refund what you paid for the phone.
These are expensive devices so they won't send out a replacement until they've recieved the original.
Some phone manufacturers will only send a new one out if they are permitted to charge a person's Credit or Debit Card first.
You could speak to Citizens Advice about this but I'd recommend to use the page I used to send the CEO Department a message.
In the UK we also have Consumer-Rights-Act 2015.
A person paying by Credit or Debit Card can ask their Bank to intervene in regards to forcing a refund.
I wish you all the best with this.
Current Phone > Samsung Z Fold³ 5G.