Mom found my birth mother without my permission [Rant]

When I was 18 (4 years ago) my mother found my biological mother through facebook and ask her to contact me. Looking back on the event I can see that she had good intentions... but I wish she hadn't done so. According to her, the adoption agency that she used to adopt me was crooked [Has anyone else had this happen?] and most of the papers/files that were used are now missing. She was able to remember my birth mother's name and used facebook to introduce us.

I'm really not sure what to think about the whole thing. I've known since I was very young that I was adopted within days of my birth and that it was a closed adoption within the US (texas specifically). I knew that I would someday be able to submit my information so that I could the files from my closed adoption when I was 18 but hadn't made the decision to do so... when my mom told me she had all the information.

Bio mom and I have been talking on and off for 4 years now and it's hard. She has another son/family and it's hard for me to understand all of her motives etc.. I'm confused and angry that my mom pushed us together before I verbally expressed interest. I would have liked to contact my bio mom later in life... rather than 18 years old since I was headed to college and there were other issues going on during that time. It doesn't help that after bio mom and I started talking both biological relatives from my bio father and mother's' sides have since added me on facebook and started talking to me. I didn't really want them to know about me so soon.

Has anyone had something similar happen to them? Should I tell my mom how disappointed I am with her? It's been several years now and I don't want to get her upset over the whole situation. I get that she might have been worried about being a "second" or "other" mom, but I don't know how to tell her that it's not her position.

TLDR; My mom contacted my birth mother and I didn't want to talk to her when I was 18.