There is no such thing as "unlimited data", your speed is your cap.
Anyway, it's understandable that your ISP will want to have a talk with you if you push/pull 10+ TB every month (in this case, you're probably violating their "no commercial service on consumer line" rule), but 250GB/month is just ridiculous.
I can see that you're a bit out of date on these issues, so let me inform you:
1) No, your speed is not your cap. Net providers are increasingly implementing "soft caps" that they don't tell you about when you buy the service.
2) If you think 250GB/month is ridiculously low as a cap, go try to use 10TB a month with most providers and let me know what your results are.
Anyway, it's understandable that your ISP will want to have a talk with you if you push/pull 10+ TB every month (in this case, you're probably violating their "no commercial service on consumer line" rule), but 250GB/month is just ridiculous.