Why do they advertise lies

Happy new year to hellopeter. Am not happy with the service of Telkom,am having a contract of a simcard that they giving me data of 10gig,so what happend was they said the contract is R99.00 permonth and i've been having the simcard for 6 months but now i have paid R900,54 cos if u calculate 99 by six it wont be 900 dat i have paid so simple telmkom please bring back my money n cancel de contract dat we having,cos u giving mi poor service n pla dnt advertise lies on de internet pls cos ur simcard said 99 per month like today i paid R301 so am tired of telkom.hellopeter pls help me so dat telkom will stop.deducting my money