Mtn airtime depleted

I have been buying the 1gig and receive the free gig for the past 9 months and its been lasting me almost a month suddenly in the past 3 Months it doesn't, i will suddenly get the depleted sms.what has changed my internet usage is the same I still use the same cellphone with the same apps. I have been seeing alot of complaints on social media which I didn't understand until today when at 3pm I had 1.6 megabytes and at 3:45 I received an sms that my data has depleted, my question is what different apps were running today that weren't running yesterday or the day before because i cant have used a gig in an hour I feel ****** and this is very upsetting and i swear if this continues i will try other networks. Please don't tell me about settings and running apps, Because theres nothing different about today's usage or yesterdays Why didn't I consume a gig yersterday or the day before.