Well, this is the answer that the OP ended up using and was his whole idea , I just post it because op does not currently have enough reputation to do it himself:
“Okay, here is the solution: I had to add another column to tablix and add a text field to it that contains the name of the department. Then I hid the column from the report and set a link to this text field inside the heading The name of the text field in tablix was named DepartmentName , so in the header I added a text box with the expression =ReportItems!DepartmentName1.Value . It works like a charm !!! "
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