Sounds like you waited until launch time to start hitting social media and do your marketing, which is the first (and probably fatal) mistake.
If you can't afford to advertise then you're starting off WAY down the line in terms of getting users. You're basically out of the game entirely. The only hope you have is to have an amazing game, something that has a powerful selling point (e.g. best game of its type, prettiest-looking, most features, unique game design, etc), and spend the time during development sharing your progress so that some buzz builds around it prior to release.
With mobile game development you're entering potentially the most heavily monetized and metric-controlled part of the industry, where almost all success is a result of venture capitalists throwing money at the problem in an attempt to flood the market and wash little guys like you away. It's so carefully controlled that even all the icons are converging on the same designs because they know that the biggest problem is user acquisition and the first thing you see is more important than the game itself.
