Automated Sponsor Reminder System

I need a simple but effective system to send automated reminders to orphan sponsors based on their annual or 6-month payment frequency. I will provide a list of sponsor names, email addresses, last donation dates, and payment frequency. The system should send reminders by email and text message at the correct intervals. Please contact me only if you have experience building similar automated reminder systems or can demonstrate that you can deliver this work. Only serious and qualified candidates will be considered.