Payment plan for phone

Hello, how do I go about asking for a payment plan for the remaining months I had to pay my phone off to MEO after canceltion my packae service with them. I did not realise if I cancel my services with them I have to suddenly pay all remaining months for the phone I bought on credit through them in one go instead of over the 10 months that I originally had. Every time I ask for a callback in English tMeo calls back and then cuts the call. Can anyone help with an email as they make it impossible to reach them. Thank you, Anja Kunert