your internet is a service that is provided by your service provider (ex: T-mobile, AT&T...). They offer different packages that have different services offered. Some of those services are limited to speed and / or Usage amount. please check that all that is in order.
No you are wrong. I got two same phone with same providers. On one phone tethering works likevit should on another dont. Problem is in settings and I cannot find out wheerec exactly.