partial service return for credit note

Hi Experts,

Already i have put lot of efforts on this issue, searched in google got many answers,raised sap reuest also but not getting exact answers please help for the below issue..!!

Service PO created ME21N : 1000

Two service entry sheets created ML81n as below

                                            A: 800

                                            B: 150

Invoice created for both service entry sheet MIRO: 950

Vendor payment also done from FI side.

Again Credit note created for : 200

How to adjust the amount in service entry sheet to make the amount equal.

If we revoke the service entry sheet then entire amount is getting reversed with Movement type102 (we have no option for partial reversal ).

From FI side they are saying they cant do anything since payment already done to vendor.

Thanks,

AMD