Many years ago I faced a similar catch-22 re: visiting the USA. Turns out that immigration had lost the exit data of visitors over a period of many months, perhaps as long as a year. I too for a long while was given no reason for increasing difficulty entering the US. And got pulled over on arrival for 'secondary inspection' a couple of times, as their computers flagged me up as a serial overstayer - I have described it on this forum before.
No could tell me why I was flagged up, until one day either US-CBP or the embassy suggested I contact one specific named man in Washington DC, and that he was 'the only one who might help you'. He wasn't anything notably senior, he was apparently the one guy who dealt with correcting erroneous records. I'm pretty sure it was the CBP officer '''interrogating''' me in '2ndary' who gave me that contact. So I called the suggested guy and indeed he did resolve the matter and very quickly. In a simple 10 minute call he told me precisely what the issue was (as above), and how I might seek to overcome it. In my case I provided several boarding cards for the flights leaving the country, where the exit cards had been lost. After perhaps a year of trying to get any answer and getting absolutely nowhere, suddenly it was resolved.
Obviously the US is not SG, but it's an example of a wall of silence existing until you hopefully find a possible channel through it.
Maybe you might find something of use in these two exchanges of letters..?
http://www.ica.gov.sg/news_details.aspx?nid=13098
http://www.ica.gov.sg/news_details.aspx?nid=12696
p.s. In your shoes I might also have a chat with him, and ask if he might have had
any dealings or perhaps 'misunderstandings' with the authorities that might count against him. Perhaps a policeman had a chat with him re: something or other. I'd want to clarify such, as that would be perhaps a simple explanation. But I'd also be conscious that if anything like that happened, he might not wish to share such things...
