Messed up debit orders and no assistance regarding Arrangement letters

We have been through the worst with a debit order system that is not efficient. As I speak, a debit order went through on the 10 of this month without any communication, yet the date is usually the 28th. Account is in arrears and we had to call in many times and being transferred to different people just to make an arrangement for them to debit our account. Lastly, I'm not sure if I am correct but I have requested for an arrangement letter of which I've been tossed and turned and have been promised that someone would send me after 3 days or so, only to be told that they actually dont give out arrangement letters. This is weird considering that the arrangement in place have been adhered to and that arrangement letter is going to assist us in getting funds to clear those arrears. To be honest I think this company has the worst communication channels and do not really care about assisting their customers. We have given up hope in ever getting any assistance regarding our issue.