Why is she like this and what can I do about it

Hi, in 2015 I got emotionally attached to a girl at work but at the end of 2015 she started dating her current boyfriend and they have been together now for just over a year. At the time they got together we spoke on fb and both agreed the way things were we would never be mates, friends or intimate so I deleted all her contacts from my life and prepared to move on.

But through out 2016 I've been getting phone calls, she's been asking me to pick her dinner up ect once when I was out with a mate she used another of my work friends to find what bar I was in and then came and found me, not only this but just before our Christmas do this year she was going round my friends at work telling them I was in love with her.

I would like to add that for my part I have not given any her any reason to suspect we can be anything but work colleagues, in fact she has had to be told 5 times how things are this year just gone each time her response has been yeah ok or I'm fine with that.

Now you know the facts, I am really looking for advice how to ensure this year does not go like the last one as we have only been back one week and she has been trying to get chummy aging and when I do not respond she switches tact and will talk about how great her boyfriend is. Any advice or comments will be greatly appreciated on how to deal with this girl. Thanks