The only way for enroute ATC to cancel a SARTIME is to write down the details on a strip as the pilot says them. The ATC then calls the data guy and the data guy writes down the details on his own strip as the ATC reads the details that they copied from the pilot. The data guy then hangs up from the ATC and calls CENSAR on the 1800 number or or sends them a fancy message on the internoodle and gives them the details that they copied from the ATC.
The faffing around is tremendous, hence the occasional grumbles.