Think Im Gettin Robbed (rear Axle Assy)

I INQUIRED ABOUT A WHINING NOISE IN MY 95 DODGE RAM VAN B2500'S REAR AXLE AND WAS TOLD BY THE HELPFUL FOLKS IN THIS FORUM THAT IT MAY BE THE DIFF. BEARINGS OR WHEEL BEARINGS, TURNS OUT IT WAS THE DIFF BEARINGS BUT WERE DRIVIN ON FOR SO LONG IN BAD CONDITION THAT IT WORE OUT THE HOUSING....QUESTION, WOULDNT A MECHANIC KNOW IF A WORN HOUSING WAS PRESENT AND WOULDNT THEY TELL ME THAT I NEEDED A NEW REAR END OR HOUSING? HE ENDED UP REPLACING WHEEL BEARINGS AT FIRST. $200. THEN HE TOLD ME REPLACING THE BEARINGS IN THE DIFF HOUSING WILL WORK FINE. $400 MORE. AFTER ALL THAT THE WHINING GOT WORSE TO ALMOST A GRINDING NOISE IN WHICH A 1000 WATT SOUNDS SYSTEM WOULDNT COVER UP. NOW HE FINALLY TELLS ME HE NEEDS TO REPLACE THE WHOLE REAR END WHICH I FEEL SHOULD HAVE BEEN DONE IN THE FIRST PLACE BUT TOOK HIS ADVICE TO CHANGE BEARINGS. NOW THEY WANT TO CHARGE ME AN ADDITIONAL $1400 TO CHANGE THE REAR AXLE. NOW AFTER 3 ATTEMPTS TO STOP THE NOISE AND $600 BUCKS, THE NOISE IS WORSE..... AM I LIABLE FOR THE $600 OR SHOULD THEY TAKE THAT OUTTA THE REPLACEMENT OF THE AXLE AND BE NICE ABOUT IT. AND ALSO, DO YOU HAVE TO CHANGE THE ENTIRE REAR AXLE OR CAN YOU JUST CHANGE THE DIFF HOUSING ON THE VAN.....SORRY BOUT THE LONG THREAD BUT IM CONFUSED ABOUT THIS, I FEEL LIKE IM BEING DUCKED.....(HELP PLEASE):banghead: