Paying for cancelled contract

After struggling for a long time to take my number on pay as you go, the account was finally closed on 22 November 2020. They sent an sms to this effect. Then on 1 June 2021 they deducted money from my account. My son is using this number on pay as you go as I have left the country. Today he gets an sms threatening to cancel the number and report him to a credit bureau. They are not responding to my emails.