I’m just wondering if my ISP is doing something or something in my hardware is not right

I use my mobile cellular data as my main internet connection at home , it’s just me and I work 12 hours so it’s not a good idea to have home Internet and I spend all my time outside so when I’m using my MacBook at home I connect it to my iPhone X hotspot and when I do speed testing I get more than 70 MB but when I’m surfing the Internet it’s so slow , I know it’s a 50-50 balance between your internet connection and the server and still I get 70 MB in the Internet is slow

What I’m thinking that my ISP is blocking something or that they are involved with something

Yes , my monthly usage is about 500GB and my data plan is supposed to be UNLIMITED