This is what I did

I had almost the same situation. A few days after the installation, I found a few boards were not installed approriately. I called the contract several times, no response at all. After one month, I left the following message: I have called you several times, and the boards post safety issue, if you do not address this within this week, I will ask a third party to fix and will send you a bill for reimbursement. This is my final message to you. " The contract returned my call in 3 minutes and showed up the same day.