This is yet another one of the spoofed numbers used by the card service scammers in their tries at defrauding us. It is wise to block, or not answer ALL unknown calls from the 305 area code-- the code of scammers!
Sandy, these particular scammers try to prey on anybody and everybody, not just the elderly. There's no reason to be fearful about them possibly using a cell phone. It doesn't mean a thing. In fact, you can't believe the number that comes up anyway because scam artists like to spoof (fake) the phone number that shows up to make it harder for the authorities to track them down. (In fact, they may not even be in the United States.) The people who run this particular scam aren't interested in visiting your home. They want to try to sucker you into giving them your credit card number over the phone. If, however, you receive a call from a stranger who is insistent on visiting your home (or one who tries to get you out of your home), do not hesitate to call your local police immediately for guidance - and mention to the caller that you will be contacting the police, just for good measure.