I need to be more ertive?

I'm having problems with 3 colleagues at work. It's a small office full of women and I want to be more ertive with them. I don't work with them anymore (used to and think they've got huff that I've moved on, it consists of a manager and 2 of her colleagues) when I go into office they are either rude or ignorant to me so I avoid going into the office when at all I can but I can't always avoid it. They sometimes have the nerve to ask me to cover when they're busy and then speak to me like I'm a piece of dirt. I want to know some good things to say to them to combat this please. Polite things only please.