Extraordinary claims require extraordinary evidence.

I don't think it's an extraordinary claim but some evidence would be nice because the comment made me paranoid

I run at AWS for 5 years and use more than 25 services and keep an eye at a huge sum very carefully year never seen this happening so it's pretty extraordinary for me. I dont ever remember AWS increasing prices for any service at all.

It really is. AWS never increases prices, let alone retroactively. They make such massive margins where they do make money they absolutely do not need to use underhanded tactics to milk their customers who are more than happy to hand out money of their own volition.

They give out hundreds of thousands of dollars in credit just so you can use their crack.

The GP's comment's claim isn't just extraordinary, it's out there with "I saw aliens and they probed me". Possible? Physically, yes. Unlikely? Quite the understatement.

Which service and whay API?

What was the service that they retroactively increased the cost of?