You can use both words together, but it means something different from what I think you're trying to say. しか+Verbない is used to express that the preceding thing is the only thing that is true.
Thus, you should understand
as meaning that the only thing that is true is
B didn't get a bonus of 1万 and certainly not over 1万. The only kind of bonus B got is a bonus that is under 1万.
If you want to express that a bonus of under 1万 is less than expected (i.e. you expected a bonus of 15万 but instead got a bonus of 1万), then you would want to say something like this: