Free Singa account
With a free Singa account, you can sing five songs per day within the app. The app can still be used to request an unlimited amount of songs when connected to a karaoke venue. Do be mindful of other guests though, and make sure everyone gets a go :)
If you have a Premium subscription but the app still only allows you to sing five songs, please first try to restore the purchase following the steps in this article.
If it doesn't help, it's possible you are signed in on another account than the one the subscription was started for. You can check your account details by first signing on your account and then navigating to Profile->Settings.
The account type you are on can be checked from Billing. If you can see a "Get Premium" button, it means that the account you are logged in with is indeed a Free account with a three daily song allowance.
You can look through the inbox of your other email addresses and see where the subscription verification was sent to, and then log into Singa using that address. When done, perform this check again to see if the Premium subscription is visible.
If needed, you can delete a redundant account and keep only the one with your Premium sub, detailed steps here. Also, your email address can be changed from Settings->Account.