How to change the phone number on my classified?

[CarSync]

Posted my classified with incorrect phone number and now I can't change it! Sent a message via PISTONHEADS website. Left messages on 020 7072 2807 and 0208 102 0509. There is no functionality on the website to change the number myself. Nobody picks up the phone it always goes on messaging and they are not replying to email messages either!