Starting a company takes time. Customers aren't just going to flock to you because you put a product out. I can't tell you if you should quit or not, but if you want to know why you don't have more paying subscribers, you should try asking your existing subscribers what made them want to pay for your service, what they love about it, and what they would do if it no longer existed. I'm sure somewhere in there you will get some interesting answers that will guide your decision on how to move forward.