Why is my 4g HSPA+ through At&t for Net10 running so slow?

[AC Question]

I have a Zte Paragon Net10 phone which uses At&t towers. My 4g hspa+ speeds are only running .5 mbps while I can run the same test on my moms Net10 phone(also 4g hspa+) and hers is showing 5-6 mbps.