Can I switch from a retirement extension to a marriage extension in Thailand with a stat dec?

I have a retirement extension that expires on May 7.

I would like to replace it with a marriage extension.

The Australian embassy in Phuket witnessed my stat dec for proof of income in early January and told me it would be valid for 6 months.

I went to Phuket immigration this morning and a volunteer informed me that I can no longer use the stat dec, although the Australian embassy insisted it will be ok.

Can somebody let me know my options please.