OK, Problem solved. I just want to share with everyone. You might need one day:
8/5 morning We called them and asked an appointment. They said appointments made by online only.
We checked their website and it showed all August is full. (they do notary only on Wednesdays)
We called them again and asked "really?" Of course no body explains how come they are full for notary service which is takes only 5-10 minutes. Or if they are this much busy, why only one day in a week?
(Mexico Embassy has every day)
8/5 afternoon: Before we purchase our tickets to Cancun (there is a consular agency)i just want to check one more time Belmapon's website. Guess what? All Wednesdays were open (for 2-3 people each day)
So, don't give up! Bother them.
Cheers everyone,