I have been recently buying discounted data in large packages for example 20gb upwards

I have been recently buying discounted data in large packages for example 20gb upwards. However there is this annoying trend they implimenting where I will suddenly loose network and be unable to access my data im telling you there will suddenly be totally no network no data access. This thing is done deliberately. Than immediately after the data is finished(expired) the network suddenly works well. We are being made fools and manipulated. In the end you wont even finish this discounted data u received. I just wonder Why is mtn frastraing us!