If you don't want this level of granularity, then remove Group Material and leave only the Month that you are using as columns.
Then, replace your formulas with an aggregation by group material:
sum(aggr([Act/Fact], [GroupMateria], Month))
I hope this helps.
Try creating a new field and use that in the pivot table
TableForExtraField: LOAD * inline [ GROUP_FOR_PIVOT, GROUP MATERIAL Natural Rubber, Natural Rubber Synthetic Rubber, Synthetic Rubber Carbon Black, Carbon Black Chemicals, Chemicals Textile reinforc., Textile reinforc. Metallic reinforc., Metallic reinforc. Total, Natural Rubber Total, Synthetic Rubber Total, Carbon Black Total, Chemicals Total, Textile reinforc. Total, Metallic reinforc. ];
If you then use GROUP_FOR_PIVOT instead of GROUP MATERIAL you'll get the Totals at the end like you want.