Data expires after a month

I am under the impression data does not expire , after a month. On the 25/11/2019 I loaded data onto 10x security cameras, R60 on each and 1x I made a mistake and put on R29( was under the impression this would last many months). On Christmas morning cameras stopped working , I loaded data again and all was well. Some cameras are set to only send 1x photo a day, while others are set for motion, and can send unlimited photos, all cameras data lapsed exactly a month, impossible. It does not help phoning MTN, we have all tried this, you hold on forever.