Excesa service tax charged under rcm

in case if vendor is not aware about service tax under reverse charge mechanism and has charged us excess, is the company still liable to pay its portion of service tax? Is there some notification that if the govt has received the full amount of service tax it isnt required to pay rcm separately? can we suggest the vendors to revise the bill in case he has charged full serv tax? in case if vendor is not ready to revise or not ready to disclose what amount has been deposited to the govt, what is the remedy?