I was so happy to see they had Uber in Bali however the drivers kept canceling on me. I heard from some travellers I met that same thing with Grab (the South East Asian version of Uber). The reason is because the local taxi drivers don't like Uber and Grab (sounds familiar), there's a lot of areas/streets where the Uber/Grab can not enter to pickup, for example airports, hotels, etc. basically where the local taxis tend to be at.
The locals suggest to use Go-Jek instead. It's a bit more expensive than Uber/grab but more reliable (maybe because it's Indonesian-owned?) you also have the option to get a scooter ride which is convenient when the traffic is bad, and order take outs :p So make sure you download it and register before heading to Bali!