rebate problem

hi gurus

In vbo1 i kept as amount 200 rs. In vbo2 rebates when am making as 150 rs. after that in vbo2 i kept status as B and I clicked on rebate payments from menubar i selected creditmemeo automatic system generating creditmemo. After that billing in vf01, I did. in this manner. When i want to give remaining 50 rupees system doesnot showing anything i have balance amount what could be the reason. How should i enter remaining amount. In which transaction should i enter remaining amont. '

Thanks in advance