MTN - Shocking

I bought an upfront payment WIFI router for my mom. Made payment on the 25th November. When trying to activate it they tell me the data will only be active on the 01st January as I made payment on the weekend and they had a delay allocating the payment. Why did I need to pay upfront in November for something that will only be active in January. The way they make you made the upfront payment is on the same day via a link. Dont know why a later internal payment allocation needs to now become our problem.