Problem with calling a module from another module

I am having trouble calling modules from other modules using VBA in excel 2016 on a mac.
In a workbook I have 2 modules:

Sub testsub()
    Call xchart(a, b, c)
    MsgBox a
End Sub

and

Sub xchart(a, b, c)
    a = b + c
End Sub

When I run the first module(testsub) I get a "Compile error. Expected variable or procedure not a module"
What am I doing wrong? I have used this construct elsewhere in other workbooks and sometimes it works without a problem, sometimes it gives the same compile error.

Calling a Procedure

• In VBA, 'those' and 'these' are called Procedures, and they are located in Modules.
• Basically, a Sub does something while a Function returns a result.
• The Call keyword is considered deprecated.
• For whole numbers (integers(math)), you could use something like the following.

<!-- language: lang-vb -->

Option Explicit

Sub MyFirstCallingProcedure()

    Dim b As Long: b = 1
    Dim c As Long: c = 2
    
    Dim a As Long: a = SumupTwoIntegers(b, c)
    
    MsgBox a
    
End Sub

Function SumupTwoIntegers(ByVal Int1 As Long, ByVal Int2 As Long) As Long
    SumupTwoIntegers = Int1 + Int2
End Function 

This happens when the module name is the same with the Sub in the same module.

'check and RENAME THE MODULE containing this Sub if have the same name
Sub testsub()  
    Call xchart(a, b, c)
    MsgBox a
End Sub

'check and RENAME THE MODULE containing this Sub if have the same name
Sub xchart(a, b, c)
    a = b + c
End Sub