Broken beach chair not being credited

I purchased a beach chair from [URL Removed] on the 11th of December. The chair only worked for the first 4 days and then it broke. We came back from holiday and I reported it and logged a return. They came to pickup the item on the 31st of December. I received and email stating the I will hear from them within 3 business days. After 6 business days I contacted them for an update and they said the matter was closed from their side. I told the lady that I haven't heard anything back and they still have my chair. Now I received a credit note, but not for the chair I purchased. How can they pickup a damaged item and not notice which product they picked up.