I looked up the carrier for my most recent spam calls using lookify.io:

1. PEERLESS NETWORK OF OHIO

2. PEERLESS NETWORK OF FLORIDA

3. PEERLESS NETWORK OF CALIFORNIA

4. PEERLESS NETWORK OF CALIFORNIA

Nothing from Twilio, but Peerless Network certainly stands out. I see they describe themselves as "A Disruptor and Aggressive Innovator".