You should not get these reminders after you purchase the software unless you purchased on a website other than ours, or if you used different email addresses to download, then to purchase. If you are still getting the reminders, just click the link in the bottom of your next reminder to change your email contact preferences, then uncheck the "Send me tips and keep me informed about my trial period for my downloads." option.
This can also happen if you are upgrading an existing version of Pocket Tunes and check the "Keep me informed about my trial period and send me tips for the products I have downloaded." option during the download process. Just click the link in the bottom of your last/next reminder to change your email contact preferences, then uncheck the "Keep me informed about my trial period and send me tips for the products I have downloaded." option and you will stop getting these emails.