Didi is the most popular car service company in China, though a few others are starting to make a pretty big dent in the market. You can download the app (Chinese or English) and link your credit card to it. You can also use didi inside of WeChat, in case you don't want too many apps. I use didi or similar about 80% of the time, and taxis the rest of the time. Black taxis are really easy to spot....pretty much a non issue.