Last Bill quantity,Bill date of customer in bex query

Dear Expert,

  We need to show last billing key figures including last bill date of customer in the fiscal period in bex query from vditm cube. So we have developed query where we set the key figures aggregation as 'Last Value' on 'Bill Date'. We do not require Cancelled bill so corresponding filters are given in Characteristic restriction area. But cancelled bill document has 2 entry in cube first, which comes initially in cube and second which come in another delta load with Cancelled Indicator = X. Second document has qty value > 0 but First bill qty become zero.

Data in cube is:

Customer      Fiscper     Bill_Date        Bill_No             Bill Qty            Cancelled Indicator

10023          012.2012    30.03.2013        101                20.0                

10023          012.2012    31.03.2013        102                0.0                          X

Customer      Fiscper            Last_Bill Qty(Aggregation-Last value)                                       Last_Bill_Date

10023          012.2012         20(last day qty in 002.2012 month)                                        31.03.2013(Formula Variable)

Here last bill date is wrong we need to show 30.03.2013 as 31.03.2013 bill is cancelled and qty = 0.

We can't change cube data as it'll effect other queries, tried to implement condition qty <>0 but its not working with formula variable Last Bill Date.

Please suggest how can we show 30.03.2013 date as last successful bill date.

Thanks,

Ankit