In that case, call again tomorrow and ask about the exact address of the company, it's full company name, the contact person's name etc. The you can do a search on yellowpages. To really check whether this company exist, do a search via ACRA here:
ACRA website
I seriously doubt it's via an agency. The agency's staff will contact you first before referring you to go for an interview. And no interviews would be conducted by any decent company at 7pm.
I suspect that it's either a direct sales or a MLM company. If still in doubt, I suggest you reject the interview immediately. You don't have anything to lose by missing out this interview.