Cutting off my SIM cards.

I use Afrihost data and when I woke up on Saturday my SIM card was not working(not the first time). I decide to call them today to ask what the problem with my SIM card is, only for them to tell me that MTN deactivated my SIM card because it hasn't made any phone calls for the past 3 months (news to me). The first time when my SIM card stopped working they told me that MTN is just deactivating their SIM cards and they don't know why. They however offered to deliver a SIM card for me free of charge only for them to bill me for it. Now I'm requesting a SIM card from them because the one I have is not working, they are telling me that they will charge me for it or I should just go and buy an MTN SIM card. How do they bill me for something that isn't my fault? I really don't understand. Now they decided to just switch off my data for what reason? I don't know. If Afrihost isn't sending you a crazy bill they are switching off your data. Why do their mistakes inconvenience me as the custome...?