Tata Docomo — Poor Internet Speed

Hello, I bought a Tata Photon Wireless Dongle for internet Services and it work satisfactory but in Month May and June , i got so poor speed that i am unable to open single page. i put numerous complain to Tata Photon but no prompt action was taken. Once a Service engineer come and improve the speed, but from the next day same issue arise. Every time i call customer care i have promise from them to take urgent action but the issue get not resolved. now the summed up bill to me for those month of the poor speed and want me to pay for them, i have three complain request numbers which i get from Tata Photon. [protected] [protected] [protected] kindly suggest.