There is no cause to make disparaging comments on this forum. We understand that you don't agree with @Mj_206 , but there is no need to make personal attacks. Post all you want, but keep it civil, as there are also minors that use this forum.
OfferUp is a small company that lacks general customer support, and is not obligated to answer your inquiries/accept your challenge. It's not like you pay an annual/membership fee or any kind for the use of the app. The app has over 40 million users and has to focus on a set of priorities. If you want to be heard, subscribed to the auto dealership program, as it even has a dedicated phone number that you can call for customer support.