How can I extend my guardian visa in Thailand if my son's birth certificate requirements have changed?

GUARDIAN VISA Question: I need to extend my guardian visa. I went today (to Chiang Mai immigration and waited 10 hours) with all the relevant documents including a notarised / apostille birth certificate (stamped by the Foreign Office in UK) of my son and was told this wouldn't do and I need to get it stamped by the British Embassy in Bangkok. This is despite the same document being adequate last year. Have there been any changes in brith certificate requirements for guardians? The issue now is that the British Embassy in Bangkok does not do this and clearly lists the services they provide - this not being one of them. Any suggestions/ advice would be appreciated. Thank you!