Unprofessional and don't respond to client queries

This company fails to respond to clients queries. I settled the account that was handed over to them, they didn't even acknowledge the payment. I was promised that I would be sent a paid up letter after 21 days and that still hasn't happened. Now, I am left chasing them for this said letter and they keep postponing it by 7 days every single week when I call to find out. Furthermore they don't respond to emails and when I do get ahold of them they said that they have a backlog for these said letters and that I should wait you guessed it another 7 days!!