HiFi Sound Connection

On Aug.24 th 2009 I purchased 2 car receivers, 6 6"x9" speaker boxes and 8 speakers from HIFISoundconnection.com . I paid via PayPal the total amount + shipping : $ 478.28
Shortly after the purchase I received 1 car receiver and the 6 speaker boxes ( worth approx. $150.00)
It has now been 10 weeks, they still advertise the items I bought on their site but obviously do not have them in stock .
Because I was too patient PayPal will not do a thing ( more than 45 days) . HIFISoundconnection offered me a store credit but there is nothing similar in store at comparable price .
Is this a scam ? Can they take your money for something that is not in stock and then give you a store credit ?
I would not complain at all if I had been charged only for the items they sent, but being charged the full amount for the items and the full amount for shipping is not acceptable .