Issue with Calling SUB with UDF - excel

Question

With the use of call statement, I am calling a sub RETURNSEARCHMATCHES that includes UDF FINDCOLLETTEROFNAMEDRANGE(string).
The code where I call the function is below:
Option Explicit
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
On Error Resume Next
Application.EnableEvents = False
If Selection.Count = 1 Then
If Not Intersect(Target, Range("SearchField")) Is Nothing Then
Call OSS_macros.RETURNSEARCHMATCHES
End If
End If
Application.EnableEvents = True
End Sub
I was debugging the code inside RETURNSEARCHMATCHES and I found out that the UDF function FINDCOLLETTEROFNAMEDRANGE(string) is not called by the sub (the code is below):
Public Function FINDCOLLETTEROFNAMEDRANGE(range_name As String) As String
Dim cell_range As Range
Set cell_range = Range(range_name)
If cell_range.Address(0, 0) <> "" Then
FINDCOLLETTEROFNAMEDRANGE = Left(cell_range.Address(0, 0), 1)
Else
FINDCOLLETTEROFNAMEDRANGE = "NONE"
End If
End Function
Sub RETURNSEARCHMATCHES()
Dim cw As Worksheet
Dim is_matchLeft_name As String
Dim is_matchLeft_col As String
Dim last_row As String
Set cw = Sheets("4c.Travel Costs (Search)")
last_row = CStr(cw.Cells(cw.Rows.Count, 2).End(xlUp).Row)
Debug.Print "OK"
is_matchLeft_name = "Is_Match_from_left"
is_matchLeft_col = FINDCOLLETTEROFNAMEDRANGE(is_matchLeft_name)
Debug.Print is_matchLeft_col
End Sub
Do you know why it is like this?
Am I supposed to pass this UDF function somewhere in the call statement?