Welcome to MrExcel,
It's hard to tell from your post how your PivotTable is organized, but here are a few thoughts to help you determine the cause.
Based on the image, I believe that one of these scenarios is occurring...
1. If you have only one field in the Row Labels area, then the items that appear to be duplicates must be slightly different (perhaps a leading or trailing blank character, or rounded number formatting). To test that, try a simple formula that tests if A2=A3 (where those two cells appear to both be "1000".
2. If you have more than one field in the Row Labels area and the PivotTable is set to use a Compact Form Layout, the first 1000, could represent the first field, and the second 1000 could be a separate second field.
3. If you have more than one field in the Row Labels area and the PivotTable is set to use a Tabular or Outline Layout, then each row of the PivotTable might represent unique combinations of the Row Fields. The first example, doesn't appear to support that, but it could be a case of the 0's not all being exactly the same.
If you can sort out which of those scenarios you have (or something else), that will determine how you might combine rows.