Head Gasket 94 Volvo 850 turbo

I had my head gasket replaced last June. Almost 3 weeks ago I took my car into the shop because it over heated and I was pretty sure it was a head gasket problem. I called just about everyday to hear news about my car but they gave me the run around. I have been VERY loyal to this shop, pretty much had my keys on retainer. After 2 weeks of getting put on the back burner I had to grab some stuff from my car, so I went down there and my car was in the back lot and snow piled on it like it had not been moved since I had it towed there. I was a little ****ed since they had told me they did some pressure tests on it. I could see that was a lie. Well, after calling and getting them to finally get it in the shop, he told me it was the head gasket and that it would cost me $1,200 to repair. I said I had that replaced in June. He began to tell me that he would lower it to $800, I said that I've been without my car for weeks and again said you guys replaced the head gasket last june. He gives me his final offer, I pay half of labor and he pays for parts, which comes to $600 from me. I said OK if they get it done in a few days and not week(s). Well, it has been a week and I'm getting annoyed with it and have not heard anything back from them.
Question:
Do I need to tell them they need to replace this at their cost? They have had my car for almost a month. Should I contact BBB? Should I pay with Credit card and drive off and call my Credit card company to stop payment? I don't want to do the last, but this is getting out of hand. Thanks for the replies.
They told me that a hose was the problem for the head to fail, isn't that a hose that should have been replaced when I got the head replaced in June?