friends?? help pls ahah

Hey so I have a group of friends, it's me and three other girls. We are all best friends and do everything together and today I got a message from one of them asking me to go to the city with them all. I asked them when they organized it and she said yesterday.

They accidentally added me into a group chat with just them and not me. Turns out they have been talking together all holidays while they haven't sent me one message. I found all of these other messages saying how they didn't want to invite me into the city with them and they had actually planned it over a week ago and one of them just decided last minute that maybe I should be invited.

They also are talking about me on this chat and stuff . I confronted one of them about it and she denied it and the other two haven't responded and are ignoring me. It's making me so sad because they have done this before and promised not to again. I feel like crying so much, they are my best friends and I am really hurt, I want to hang out with them but they are making me feel like shit. I need advice :(