I bought an item from Facebook a few months ago and suddenly lost my job due to unforeseen circumstances. The original payment plan was to pay the person monthly, in their words, "whatever I could afford". I was very upfront about my personal issues and made sure they knew when I could not pay them back. When i first bought the item they wanted me to sign a contract but never sent me anything of the sorts. Can they legally charge me interest without giving notice that it would be something they'd do in the event I could not give them any payment?