Variable isn't being recognised and I'm not sure why?

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Python

def errorgenerator():
    #Generates error messages and submits to the support team
    counter = open ("reports/counter.txt")
    counternum = int(counter.read())
    counternum = counternum + 1
    counter.close()


    counter = open ("reports/counter.txt", "w+")
    counter.write(int(counternum))
    counter.close()

    print("Apologies, we can not solve this issue. Please contact the supplier, to do this please leave your email to be further contacted by the supplier")
    email = input()

    print("Thank you, your error code is " +
    counter = open (("reports/report-" + int(counternum) + ".txt"), "w+")
    counter.write(email)
    counter.close() )

This code is supposed to create an error code with counternum + 1 and then write that in a file alongside the user's email. For some reason, the code will not recognise the 'counter' in counter.write(email). Can anyone tell me why or how to fix it?

What I have tried:

I have tried writing the counternums as str and int but to no avail. Those were the only things I could think to change.