Data not being delivered as prmoised - again!!!

This is the umpteenth time that I am complaining about and to Vodacom. I have a contract which stipulates that I receive "x" amount of data every month. Since the renewal of my contract in November 2016 I have endured endless problems in that I do not receive the correct amount of data as promised. I have to resort to calling Vodacom every time and the problem get's sorted out, only for it to happen again the next month. I had an issue with my data last month, (Nov 2017). After countless calls and follow-ups I finally received my allotted data bundle. I was once again promised that it will not happen again. Well - here we are on 4 Dec 2017 and I once again did not receive my data. And once again I have to follow-up with Vodacom. My bill is paid on time, without exception, every single month!!!!! Why can Vodacom not get my data bundle correct?????