Careful with that thread.
The ThaiVisa thread is from 2008 and I believe that since 2009 you cannot extend at that office anymore but rather you need to go to the main government complex at Chaeng Wattana. I am pretty sure they moved the 90-day reporting and extension from Soi Suan Plu to Chaeng Wattana.
In short: Your hotel cannot help you. You need to either exit Thailand and re-enter or apply in person at Chaeng Wattana.
See here:
http://www.immigration.go.th/nov2004...?page=location
In case of extension service please contact immigration office in your residence area for example if you stay in Bangkok please contact Immigration Division 1 at Government Complex Changwatana.