Second hand laptop returned to the store

Lewis stores Nigel, my dad bought a laptop at Lewis stores Nigel in June 2020 we found out it was a second had laptop, was told the total amount would be reduced, we could not afford to pay it because my dad lost his job on the 1st of September 2020, we then return the laptop to the store, to our surprised we thought the deal has been canceled but we still receiving letters that the account is in arrears, why are we receiving letters when the laptop has been returned to the store