No customer service

I previously lived in Voula, a southern suburb of Athens. Almost three years ago, we moved to Kifissia in the northern suburbs. I just received a letter, almost three years later, from OTE telecom, warning me they will cut my telephone line if I do not pay an outstanding amount of 68 euros from the Voula residence. I have no objection, but I want two questions answered: First, how can it possibly take almost three years, when I closed the one line in my name and with the same name opened a new line, my cell phone never changed number, you have my details and know where I live? Secondly, I closed the account according to the proper procedure, by going to OTE and with payment of all outstanding calls. How can this amount come to be? How, when they cannot even produce a bill, just a letter stating I owe them?