It is not very clear what you want to achieve by looking at the sample data and the problem statement. Could you elaborate more on exactly what you are trying to do, possibly adding a snapshot of target state?
Here is my approach.
Use LOD to create amount x user x month value as dimension.
[Amount User x Month]
if [Amount User x Month] <1000 then "0-1000"
elseif [Amount User x Month] <2000 then "1000-2000"
elseif [Amount User x Month] >=2000 then "2000+"
If you put filters, don't forget to change them to context filter.
Group_by_Amount_SM_9.3.twbx 40.0 KB