Data Range in Chart

I have designed MI Reports that has three bar charts on it. The source data of Charts correspond to three different excel sheets.and the data in excel sheets come from userforms that I have created.

My problem is when I select the source date of the charts and starts putting the values through user form then charts display right result but when I delete all records from the three sheets then the sorce data range in excel charts changes automatically.

And then if I start putting values through userform then the charts will display few values only and the source data range changes to $A$1:$A$3 .depends.

I want to fix the source data range to 15 records.and it should n't change if I remove values from th sheets.

Can anyone plese help me out
Regards
Aman