Have I gone too far?

I was at Uni today when I got a text from Grace saying:

"Chris r u at home? Can we come round and send some e-mails?"

I replied:

"I'm not at home at the moment. I'm gonna be in the library for a while, want to get this done. I'll be home when I'm done."

Believing that they'd leave it at that. Oh was I wrong. Instead, because THEY wanted to send e-mails and use MSN (and are too lazy to walk to college) they rang my house to see if anyone was in, asked my housemate if they could come round and use my internet (I pay £18 a month for it) and proceeded to do so. Now Grace and Liz can't understand why I'm pissed off!!!!! Why bother asking me if you're gonna ignore me. Granted I didn't say "no you can't go round" in big capital letters in my original reply but to me my reply says "I'm busy. Wait a while"

So anyway, I was round at their house dropping something off when they come home and tell me this. They asked if I was cross (implying that they knew they'd done something wrong) and I initially said no it's fine before turning around and admitting that it wasn't, I'd've preferred if they waited until I got home instead of ignoring me and that I think they'd gone a step too far, before leaving the house. I think I was right to do so but I'm regretting it now.

Grrr - Liz is texting me to apologise but she said "I'm sorry for what we did" which I'm reading into as "I don't know why you are cross but I'm apologising anyway."

I'm angry because I feel taken for granted. "It's okay, Chris won't mind if we ignore the fact that he's not in and use his internet anyway." WRONG. :P

GRRRRRRRRRRR....I'm gonna eat and watch CSI. I was gonna have Grilled Chicken with Frozen Vegetables but I'm gonna put some Potatoe Waffles in the mix too to help me calm down.

Mmmmmmm, Potato Waffles.....Yumm