Fix my Delivery mobile app

I hired a team of app developers last march but it turns out that it was not a good decision. they delivered an incomplete app that still requires many hours to finish it. The app itself is functional for what it is supposed to do but there are many bugs when it comes to database management and payment issues. The app was submitted to Apple and google and was approved. I recently decided to part ways with the developers and they handed me my source codes. I am looking to work with someone that is experience in IOS and android Native languages. I am also looking to work with someone that is fluent in english so that I can accurately communicate with that person. The name of the Application is VanDelivery and can be found both in the Apple and google Play store. Please DO NOT Contact me if you havent looked at the app or are not an experienced developer. This is not a project for rookies.