I'm the founder who bought the testimonial.io domain.
You really underestimated the value of a SaaS, with 6 subs contributing $3,600 ARR, a business will have the chance to be sold 10x at $36k. I can easily recoup my investment from an exit offer, and the domain itself has its investment value too.
Look things forward, not backward! A twitter account has 43k followers today maybe will have 430k followers next year.
429 is fine, even Cloudflare has an outage just a few days ago. For me, it's just learn the lesson, fix the bug by simply upgrading the plan, then move forward :)