The customer has already paid for a dedicated bandwidth. If the ISP has used an outdated model that doesn't account for current usage, that's their problem. That's how business risk and models work.

They can, and should, respond by modifying their plans accordingly. Once the consumer's contract is up, renew them with a more modern usage model. Until then, you eat the cost for not doing your only job.

The theory that "we didn't build in a margin of error and therefore someone else is responsible" is dangerous to society.

ISPs SHOULD see losses. Their investors aren't entitled to guaranteed profits.