Go to the Vodacom website and check the coverage map. In most cases, you can estimate where the tower is. You'll notice circular coverage areas dotted all of the place. The tower will be at the center of the circle. Of course, some areas will have overlapping circles, and depending how many circles overlap, it becomes more difficult to determine where the center is. But check for your area, it might be simple. Then take a drive, and physically look for the tower, note that address or GPS coordinates, go back home, and point your antenna in that direction. You can plot your house GPS coordinates and tower GPS coordinates on Google maps, and it will draw a line between them. Use this line to guide your positioning. Check the signal bars on your router as you move the antenna around, it should go up as you get closer to the center of the cirlce (i.e. the tower), and go down when you move further away. If your router doesn't have signal bars, you can log into it's web interface, and look at the signal values, usually given in decibels (dB). The lower the number (will be negative) the better the signal.
You should be able to get a more-or-less good position using all of the above, without Vodacom's help, and in less than an hour. It will also be less frustrating and far quicker.
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