The billed me twice on two different payment metho...

The billed me twice on two different payment methods for a phone I bought. I tried to switch payment and instead it ran both. I couldn't cancel one as it was to late so I was going to return it. That went fine. I was trading in a current phone to get money off. Because the system bought me two phones I received two trade in kits. After all of my conversations with Google support they NEVER specified that I had to use a particular trade in kit. (Bear in mind I "purchased" both phones same day but all four things arrived randomly) I sent my phone back. And because it belonged to the purchase I returned. They gave me store credit. Flat out refused to reverse the store credit and put the credit for the phone on the card used. Refused to send me paperwork stipulating they had the authority to do this. Now I am out 405 dollars. I used to love Google. But this is ridiculous. Your system messed up so I get store credit...... please explain how this makes sense. Horrible customer service. Refused to tell me why they couldn't do it. Just that they won't.