Cell c's Lte con

For months I have been monitoring cell c data as I'm should get 10 anytime gigs & 10 night time gigs but I only average about 3.5 gigs so where is the data going. This isn't all, when I bought the zte router with sim the so called sales person said I would get between 50 & 90 mbs but you can't stream or do anything because it soooo slow. I have been checking the speed 18kbs down to 10 b/s. A tortoise walks faster than this. I have 2 months of this con artist contract. I will never be conned by cell c again.