OVERBILL ON A PRICE LOCK

Good day

please be advise that im not happy with the multi choice, you guys advertise the price lock, since i took out the price lock last month, i get over billed, the price lock is 549., February i get billed R1 600.00, this monthjits R1400.00, for the premium package, this is unacceptable, i dont understand how you system bills a person, that is double the amount i singed up for, and im failing to get help from the call center as they not the ones that does the billing, but rather telling me that is how your system calculates it, this is ripping a person of, not even the full package cost that much, this is not acceptable, i cant go though this every month, cause you guys know exactly whar PRICE LOCK means