Stop stopping playback on songs that are supposed to be free on people who can not afford to take another bill on.
You offered a free service that is not perfect and is sometimes not correct to those who can not afford to pay. NOW HONOR that or it makes your business look shabby and 2nd rate. The business model should have been better thought out if it has come to stopping playback to beg. Solution is obtain sponsorship to upgrade services while keeping free service. If you enhance the premium membership you will be more likely to get paying memberships to increase. You are trying to generate revenue from a source that would already be paying if they could. This is not a root cause analysis determination for revenue. There is nothing wrong with the free option. Make your better option better and if need be just add onto it making it a Gold standard option. Every 3 songs I am stopped with the plea to upgrade. Sometimes I just quit altogether because you can not get a good session in due to that. You might also consider who is on staff to for continuous improvement for your business. That might be an area to upgrade to someone or someone's with a better understanding of a business model and expansion of product to ensure success. I am semi retired on a fixed income and for me it is either the free option or no option. Or a third option.....get a part time job to pay for this which to this point has not shown enough perks to consider such a crazy thought. You have a fine product. product idea, and business model in place. Do not lose it to lack of vision in further development by simply obtaining all who use to pay. You can enhance without alienating and losing users.