rear defrost problem

my 2008 was involved in a accident and it shattered my rear window. The body where it was fixed replaced with a new rear window. When I received my car I waited for weather to fog or frost it and when it frosted and switched it on the defrost did not work. I noticed there was frost inside the window and noticed the tab for power was of the grid. Took car back to body shop and they glued the tab back on the grid. Waited for weather, defrost did not work. Took it back to body shop an tested the power from the switch to the power connection to window and test light lit up. Body shop ordered another window from their supplier which is a General Motors dealership and waited for the new glass to come to install. It was installed and waited for weather then switched it on and did not work. I looked at the connections and noticed the negitive tab was off the grid, went to body shop and they glued it back on. Waited for the weather switched it on and did not work. Told body shop I was going to talk to my adjuster what else I can do. I search the internet and found that I can use a multi-meter and test for voltage and power. Did that and meter showed over 14 volts and connection and the rest of the grid. Maybe the person doing the body work did something. Help