What are the best ways for Americans on social security in Thailand to send yearly information on time despite slow mail services?

It cannot be completed on line. Unfortunately they are not that far advanced lol.

I had to do the questionnaire one year before I moved from Thailand after that and it was a mess.

I returned it same day by registered mail Thai Post . When USPS delivered it , it was scanned and signed for.

A few months later I received the form again with a letter saying the first one was never received. I called the social security number where the form was mailed to. Person confirmed first one was never received. So this time I sent it EMS Thai Post. It was then scanned delivered by USPS with a signature.

I called the office where it got delivered a few weeks later. The person insisted neither form was received and my payments could be stopped.

I then contacted the FBU at the US Embassy in Manila. Five days later I received an email. It said they contacted social security and they actually had both forms. The original I sent and the replacement one