Data usage

I have recently been having a data usage issue started last month when I went over which never happens because  it is one person and no working from home or gaming.  Now again this month it's happened  again.

I have been on the phone for probably over 16 hrs if not more trying to resolve  the problem.  Even bought a new modem.  

I have not received any help as they're trying to blame me yet none of my habits have changed . 

I usually only uses maybe 800 a month now its going over 1300 and they're not resolving it. Especially  considering they can see there is obviously a problem on their side.

I need help I can't afford to buy a new modem considering the problem isn't resolved. I shouldn't have to switch to unlimited because  I never used that much data.

Their employees are getting ruder and ruder and not helping. 

Please give me some advice

They do not want to investigate it and keep saying it's because  I have my own modem.

Yet they cannot provide any information on exactly when all this data is being used. Data being used on days I'm not home and they can't explain that  either.

I work as a nurse I am not home enough to use the data.