learning to say "no"

i need to learn how to refuse others (firmly).
i'm the kind of person who will give in, if you manage to milk my sympathy.
well, there are people who ring up asking for an urgent reconnection.
citing the following reasons:

"old lady at home, no electricity, so she's taken to lighting candles, might burn the house down"
"has 2 young kids at home with high fever, the kids need the fan"
"1-month old baby at home with helpless grandmother"

strictly speaking, we're not supposed to grant them an urgent reconnection.
but you tell me, how can i say "no" to all these (lame)excuses, that tug at your heartstrings?
most of these reasons turn out to be complete yarns, but seriously, sometimes you just can't afford to take the risk.