Does data rate depends on Frequency not on BW?
The value 900MHz and 1800MHz refer only to the carrier frequency. A pure perfect sine wave doesn't transmit / carry any information. Only when some parameter of the carrier changes, is data transmitted. This process is called modulation. The parameter could be something like frequency, phase, amplitude etc. More frequently you change the parameter, more data gets transmitted. The frequency with which you modulate the chosen parameter determines the bandwidth. So a signal with higher bandwidth transmits data at a higher rate.
Two signals with same bandwidth and modulation scheme at two different carrier frequencies transport data at the same rate.