Data disappears nearly 1 gig at a time; scandelous

********** 618 For years i was using 3 gig a month and it was sufficent for me, then a couple months ago , i get notices near monthend that my data is running out. It in itself is rediculus because i am the only person in this house and access to the computer, June 2017 i ran out of data, and again in July so in August i watch myself but it still disappear and the morning of 21ste of August i had bascally one gig left nd a couple of hours later, not even 4 hours, when i tried to get into the network , i couldnt and when i check my balance it was gone. one whole gig without the computer being on. now on the first they give me a starting balance of 3.87gig. where did the .87 appear all of a sudden. I want about 4 gig to be loaded bac leaving me wirth a balance of 7 gig, and this disappearing data to stop now!!!!!!!!! I notce on face book lot of people complaining, i have never in my life experience this