Curious.com interview questions

Several weeks after I sent in my resume (I had already assumed they had just rejected it by this point), I got an email saying they "loved my experience" and wanted me to complete a homework task based on which they would give me a phone interview. I completed the task, two hours or reviewing videos, breaking them into parts, and writing questions to go along with them. That was fine. Was actually really fun. But then when I got to the phone interview, the person who interviewed me seemed very disinterested, which is not my typical interview experience, but still OK. Whatever. Then, they hired someone else but offered me an Amazon gift card as compensation for the time I spent working on the assignment. Now this is what really pissed me off: they never sent that gift card. Even after some gentle prodding. Now I understand that sometimes companies hire someone else. Sometimes interviewers are bored and pre-occupied. Fine. But when you offer something as compensation for work that you actually did, it seems to me that it's pretty unprofessional to then not send it.