An app has no value to anyone when it is half finished. When you are stuck in this pit of misery, you will find that the following pieces of advise will help tremendously:
Switch from hourly pay to fixed rate, if you have not already.
This will protect your downside and allow you to sleep better at night. Hourly rate works when the contractor is fairly competent and has prior experience with the stuff she/he has been assigned. For example if you are working with custom keyboard, go with hourly rate if the developer can show you a custom keyboard they have built in the past.
Get rid of features that are not critical but have become a bottleneck in development.
Better to have a functioning app that’s ready to sell but lighter on features than you expected. You can always add features later. The alternative is longer delays and possibly failure to ever release the app. Often times, people will find it very hard to do this because of emotional attachment to their vision. Let the logical part of your brain take control here.
Break down rest of the development in smaller milestones or sprints
It will be much easier to track progress this way. If issues start popping up, you could go back to the last working version and troubleshoot forward from there. This will not usually need any tech expertise and therefore you can be much more involved.
Pay a consultant
Hourly sessions with consultant who can offer guidance and possibly rescue the app will be invaluable. Maybe they can look over your code and figure out problem areas or they can vet the contractors and help you find better ones. Do not be afraid to go for high end consultants who are experts in the field. This is money well spent.
Consider changing your development team
When all else fail, consider hiring another developer or team who can pick things up from where they are and finish your app properly. Usually developers prefer not to work with other developer’s code but you should find the suitable candidate if you are persistent . You may get your previous development team to help with the switch.
Giving up on a project when you have put your mind and money into it will set you back a long way and you will be extremely reluctant to start a new venture in the future. Keep in mind that roadblocks are to be expected in any entrepreneurial endeavor. You just need to have the right mindset and the right information to keep pounding through these hurdles and you will eventually taste success.