Expiry date unrealistic

Early December had an problem of mega bytes being deducted incorrectly as Vodacom informed the last purchased is deducted first and first last, put my dissatisfaction here and the response was good. Vodacom said they aware of the problem bare with them working on it. they rectified it in the interim manually. Gave extremely satisfactory reply here. However was not aware of expiry dates applicable again. Since beggining of new year when checking balance says expiry date is 07/01. There are 998.77 mb left on my number ********** 763 my question and complaint is why do I have such n short space of time to finish that amount of mb was not informed initially of this. Only problem I have seems to centre around data, which is expensive and need it for my work urgently. Why is time frame not unlimited or at least 6 months, there should be no expiry on your purchase until finished, however leave that for now. It is mine why expire, it makes no sense besides Vodacom wanting continual purchases to boost their budget and hurt mine. I want to be able to only use what is mine satisfactorily and not enforced into an situation i have no control over. Ask no favours besides give me a proper reasonable time to use what is mine no freebys only mine. I first try all avenues before here but sadly the call centres hands are bound and those escalate it too are not user friendly at all unlike the people assisting online here. WHY always to an extreme.