Seems a damned if you do, damned if you don't scenario.
Plus, unless that was part of the contract, why do you expect it? They're a company, you get what you pay for.
At that point, it was just email, though, and not other files.
Despite that, I still managed to run out of space a while back and had to start deleting emails that I didn't care about. I was quite disappointed in them.
You do see how that can't possibly applying to literally everyone, right? You can't use the argument that "they said it would grow with me" to store 1TB of emails and be surprised when they start charging you.
15GB is a lot. Even if you receive 5 emails with 1mb attachments every single day, that's still almost 10 years. With normal text emailed, you will never run out until you die. Most cloud providers give 5GB. It's fair to say that it has grown with you to a reasonable storage size. If you need more than 15GB, it's fair to say you're beyond that.
I have an account that received only LKML. So just text, not a single attachment. And all written by humans (although many of them and some copying.) The account run out of space after ~ 7 years of LKML.
(Need to check whether the limit is really 15 GB. I think it stopped growing at 4 or 6 GB.)
Admittedly I don't know many cases with such a traffic.
The irony is that Gmail cannot delete more than a couple of thousand messages from Trash/The Bin in one go. It says "All messages deleted", but when you refresh you see that it's not true. You need iterations. I guess they are using something what AWS calls a lambda to empty the bin (don't recall the Google term) and that job hits a limit.
Yeah, I don't use that mailbox for anything serious at the moment. Just an experiment...