MTN and Mweb are Cheaper!

I signed up for a data package - 2gb data with router for R120. This was approximately two months ago. Now I see MTN and MWEB is running their special for 2gb data and router going for R89. So for a similar deal (if not the same deal), MTN and MWEB is R30 cheaper? I suddenly feel like I am being overcharged. I have received no feedback from Vodacom in this regard. So I take it its my stupidity for signing another contract with Vodacom.