MWEB not honouring promotion.

Happy then real upset. So I signed up for the Rain LTE double data promotion at MWEB. It said sign up for Rain LTE before November 2017 and receive double your data till November 2018. So I did a number of cap increases for different months with no issue and when I wanted to increase my cap for April 2018 they said that the promotion was not available anymore even though the original promotion stated till end November 2018. MWEB is not honouring it's promotion and now are saying it was until stock lasts. This does not make any sense. I contacted Rain and they said it is between me and my ISP even though this promotion was carried by different ISPs. So to me it seems that it was a promotion that was initiated by Rain. This is not how business are conducted.