Deleting specific line from a text file in Python

Question

I am having difficulty deleting a specific record from a text file when using Python.

I have a customer CSV file which has four records. What I would like to do is ask the user to select a record by typing in the customer ID and then using that to find and delete the record, however, the code I have currently deletes any line with the entered number.

This is the code:

def deleteCustomer(login):
    print("\n***********\n Delete a customer\n*************\n")
    with open ("customers.txt") as f:
        print("CustID\t Name \t\t\t Customer Town \t Customer Tel Number")
        for row in f:
            field = row.split(",")
            custID = field[0]
            custFName = field[1]
            custLName = field[2]
            custTown = field[3]
            custTelNum = field[4]

            print(custID,"\t" ,custFName,custLName,"\t\t" ,custTown,"\t" ,custTelNum)

        while True:
            with open ("customers.txt","r+") as f:
                new_f = f.readlines()
                f.seek(0)
                searchID = input("Please enter the CustID you wish to delete :")

                for line in new_f:
                    if searchID not in line:
                        f.write(line)
                    f.truncate()
                sleep(2)
                viewCustomers(login)

When I run the code it will do the following:

***********
 Delete a customer
*************

CustID   Name            Customer Town   Customer Tel Number
1        Jamie John      London          01792883844
2        Jim Jones       Paris           01792885877
3        Bob Jones       New York        01523654785
4        Alf Fisher      Cardiff         01452365896
Please enter the CustID you wish to delete :

If I enter 4 then it will remove every record apart from Jim Jones as he does not have a '4' in the field.

*****************
 View Customers 
*****************

CustID   Name            Customer Town   Customer Tel Number
2        Jim Jones       Paris           01792885877

 Returning to the main menu in 3 seconds...

Where have I gone wrong?