I think I just got scammed by a mover, and my stuff is in transit to the destination. What can I do?

So I am moving from LA to SF and I hired this mover call USA relocation and storage. (btw I found out they are blacklisted and has a F rating from BBB) the initial quote was about $1500 for 3000lb. And I am moving about 2 bedroom worth to a 1 bedroom apartment. So they arrived at my house on time and 3 guys started to rewrap + box a lot of things (this is a extra charge that I didn't really authorize) they were fast and efficient. But after it was all done, one of the main guy came and said, "I have been doing this for long time and I think it's all gonna weight about 9000lb". I thought this is a bullshit! He also said that all of the packing material cost about $700. And if I take them this to weight station, he claimed it's gonna cost more.then he said he is gonna help me by letting me pay flat rate. 5 grand!!! I haggle the price with him to bring it down to $4500. But I think it's still way high. But I was too exhausted to fight and I said ok. So I put my credit card number down and paid half first ($2250) and now they are on the way to SF. So my question is everyone is what can I do to stop them or to pay the rest of $4500. Can I notify my credit company about this scammed? Should I call the company. Should i someone(cop?) with me when they drop my stuff in SF? My only concern is that they might dump all my stuff on the street and leave. Can my moving insurance do anything. (I have full coverage on this move). What can I do??? Please help!! (sorry about the typo' I'm writing everything with iPad)