You suck and that's sad

Last week, for some reason unbeknownst to me, I was transferred a call from customer service. The lady on the phone had a great rate for her newspaper and was wanting to get the same rate to buy it for her son. I suppose they transferred her to me because I work with solicitors and know what promotions we have available, BUT customer service also has access to those so they can sign up people who call in about them. For whatever reason, I got this call and I didn't know if I was supposed to or not, but I went ahead and signed up the son on the same rate- nothing at all like what the solicitors are selling.
Turns out, once I put it through, because it was such a low, outdated rate and we've had price increases lately, the total cost ended up being about $4 a year more than what I had told the lady. Perhaps I should have caught that and called her back, but I didn't bother. Well, yesterday, I was transferred a call from someone asking for me by name. It was the same lady. She was so upset because when the bill came it was $4 more than what she had agreed to and already sent in. When I looked up the account, it changed what she was paid through by about 6 weeks from what I had told her over the phone. That's a lot, but not really when you are looking at it compared to the whole year. I explained to her what happened and apologized. When this just made her want to yell at me, I calmly told her that his account was paid through a certain date and she could go with that or I could stop it and send her money back (dumb me, I didn't think until I was on my way home yesterday that I could have just credited her the $4 and made it all fine, I think). She decided to keep it but wanted to be sure I knew how unhappy and disappointed she was about that.
It's $4 and 6 weeks lady. I'm sure you can get over it no matter how poor you are.
It should have been easy enough to blow it off and call it done. But, being me, I'm still feeling bad about it today. I was getting over it until...
Some of these solicitors seem to think I'm like their personal secretary. It's okay. It's kind of what I do and I am their contact person. Some of them are even really nice and then I don't mind helping them. But, today, one sent me an email asking a question I had to check with someone else about. I thought I knew the answer, but given that it's not really my thing, I thought I would just double check. The person I asked was more annoyed by the solicitor than me, but I still felt like she was kind of rude. Why do I get stuck in the middle of these dumb things?
This wasn't the only thing I was put in the middle of today and even when people are nice enough about things, I get stuck doing the "grunt work." And one person, I was offering to help and I still feel like I was bugging them!
I quit.
(I've been trying really hard to stay positive, so let me just throw this out there and then I'll go on).