Hi, I'm on a Smart Visa I have to renew next year. You could try asking on the chat on the smart visa site, they are usually quite helpful. I was under the impression that the place where you make the report is the same as the place where you would collect your renewal confirmation, the OSS one stop service center. I'm sorry I can't give actual experience.
One question for you, when you left and returned to Thailand, did immigration at the airport stamp your passport with an 'until date' of one year after the date you returned?