How to avoid duplicate entry in column based on multiple columns

[heerproperties]

Hello

I have one table  Name "PSV SVC SHEET " where i need to add Mutiple contact nos of customer in mutiple columns   as mentioned below

Contact No.1

Contact No.2

Mobile No 3

Now sometimes i get repeated enquiries of customer and i dont want to add duplicate entries. so i want to understand how can i avoid adding duplicate entry if any number already exisit in any on above 3 columns,  In short if any number already exist in any of above column it should show duplicate entry while adding in any cloumn in new form 

I am using this valid if,  Its wobut is Only limited to One column

NOT(IN([_THIS],Select(PSV SVC SHEET[Contact No.1],[Contact No.1]=[_THISROW].[Contact No.1])))

Please can anyone guide and see to this 

Thanks and Regards

Vijay Bhanushali

[Steve]

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