Data disappears and vodacom fails to assist

We contracted with Vodacom for data SIM over online application and approval for 40Gb, that is 20Gb for day usage and 20Gb for night usage.Since last month of August,Vodacom would load data on the SIM on the 1st day of the month and then after 3 days,I would receive a message stating that the data is below 8Gb.I asked my spouse to contact Vodacom since the contract is under her name and she could not.And then this month of September the same incident occurred and she called vodacom to give more details about our data consumption,and the consultant since promised that she will send a reference SMS and escalate the matter but even today wee are still waiting for vodacom.