Poor service delivery

Bought a couch on Saturday they told me that delivery takes 48 hours so due to work I told them to deliver the next Saturday now that I see that I’ll be home during this week I called to move the delivery date they tell me it’s impossible to change the date??? How is that impossible? I already bought the couch and I can’t cancel because they will charge me 10%. I need to know why can’t they change the date as I am the customer and they should deliver at the date that is suitable for me. Am not happy