Best way to contact Chevy with a complaint?

I’ve got a Chevy Colorado that the dealership decided to replace an alternator to fix a groaning noise. Turns out that wasn’t the issue. The truck went back in and they think they found the issue, but told me I’d have to pay for a different replacement and wouldn’t refund the alternator cost. The alternator didn’t fix anything and it didn’t need a new alternator, so I paid for something they never fixed anything. Is it better to contact corporate (and if so should I go via the main website), or just go straight to the BBB? I’m generally not a person that lodges a complaint, but 1K is insane for something that made zero difference