Quick to keep money for interest on items return - THEFT!!

Bought a couch from house & home in East London, it has been returned to them twice. After the 2nd time of having issues we requested a refund. They have refunded us but minus 2k for interest?! We paid 2 months instalments and a deposit amounting to over 5k and only got 3,4K back as a refund. And of course the people in the branch cannot explain why we’ve had to pay for interest on faulty couches. Absolutely disgusted with the service or lack their of and the attitude of “I don’t know” from the staff. Waiting for Monday to get in contact with the head office so they can explain in detail what this money is for. Money that has been ******!!!!