Cellc doesn't even know what is going on in their own company if they ask the client who paid up a account why I was issued with a paid-up letter

Emailed them my paid-up letter that they sent me and they asked why was I issued a paid-up letter and said I must send them proof of payment I sent it to them they respond by saying what is your number for further information. I've still not got any phone call from cellc.