An uber driver is stalking my 20 y/o sister

I got an Uber for my sister last weekend. She got picked up and told me the driver was flirting and asked for her number. She’s very shy and definitely doesn’t know how to turn someone down in a situation like that. Well the next day he asked if he could drop a “gift off” for her. So now he has her address and is blowing her phone up all day long aggressively asking when he can see her. I’m shocked this is happening. Advice?