Changing Commission Prices AFTER You've Paid?

[sebelrai.livejournal.com]

EDIT: Okay guys, something really weird just happened here. One of my friends just got on MSN and told me that they had told said artist that I reported them to A_B. And they up and deactivated their DA account and everything >__>; They seem to have run. Their account is now gone, but their email address is LRSS93@aol.com. Oh, and since people are asking, their DA was 'shadyah-phoenix'. 

EDIT 2: Just got the following email from them. The thing that's blotched out is my real name.

 Hello A_B. This is my first post here, so please correct me if I am doing anything wrong @__@ Anyways, since I'm just looking for some advice, I'm going to keep the artist's name anonymous for now (but if the problem escalates, I'll edit and name them, but as far as I can tell, they have not done this to anyone else). 

About 4-5 weeks ago, I commissioned an artist on Deviantart for a fully-coloured copic illustration. Their prices were a bargain based on their abilities, so I went ahead and bought one. They said they only took cash through mail, so I sent them a money order and they noted me a few days later saying it arrived there safely and that they would begin work soon. 

Now a little later, they sent me another PM saying that some personal family issues had come up, and that my commission would be delayed. I told them that was fine, and I didn't hear from them for about 2 weeks. 

Now, just a bit ago, they contacted me and said that my piece was finished but before they would give it to me, they wanted me to pay them additional 10$ for the delay in completion, and another 30$ because they had raised their prices since I had commissioned them. 

Mind you, the delay was on THEIR part, but they're charging me for extra money....? Not to mention, that 15$ was the original price they OFFERED to me for the commission, and now they're saying that it wouldn't be fair to others who buy from them, so I have to pay the extra amounts that they added....

At first, I just requested a refund and for them to simply rip the picture up, though they are refusing. Now I am just a bit unsure of how to go about this situation. I don't really care for the picture anymore, but now they are hounding me. I simply blocked them on DA, though they somehow got my MSN messenger name and my email, or will have 'friends' of theirs send me things in their place. 

 

Any advice you can give me guys?

 

Screenshots:

Agreeing to the original comm price of 15$: http://img263.imageshack.us/i/note1k.png/

Note they sent me about their 'family problems': http://img508.imageshack.us/i/note3.png/

Asking me to pay the extra money (their original note is on the bottom and my response is on top): http://img191.imageshack.us/i/note2i.png/