Uber App leaves little room for error reporting

Uber has no mechanism for you to contact them to complain other than their set menu in app. They also have no contact number. I added a tip at the end of the ride since Uber didn't show my initial tip that I included when I booked the trip. The app/website doe not allow any contact for me to provide them this detail. Terrible way of dealing with your customers, especially when app misrepresented final cost.