Monthly price in Tanzania

A dedicted 64kbit/s down carrier would cost about $448 per month.

A dedicated uplink carrier of 10kbit/s would cost about $70 per month.

You have some shared arrangement, where your downlink peak burst rate is limited to 64kbit/s maximum, so the overall effect it similar to a share of the simplified dedicated capacity described above, whose total cost to provide is $518 per month.  

( Note that in reality your terminal is most likely to have something like a continuous, steady, 2 to 27 Mbit/s downlink and an intermittent, bursty, TDMA 64k to 256kbit/s uplink.  The downlink is divided amongst hundreds or thousands of terminals.  The uplink is time shared amongst perhaps 10 to 50 terminals.  The sharing arrangements are very complex with many subdivisions and even dedicated capacity to certain sites being possible. )

If you are paying $150 per month then maybe there are intended to be 4 sharing, so that the income 4 x $150 = $600 exceeds the $518 cost of providing the service.

If you are getting 64kbit/s for long periods it is likely that the other sharers are presently inactive or have not yet been installed.

Best regards, Eric.