Poor Service from Hammond Pole and no on willing to assist

What horrible service from your Hammond Pole. I have been trying to get a settlement letter for an account that was settled on the 24 July 2017. Over the past couple of months several calls to you have proved futile. What is even more shocking is that the very same account that you have failed to provide proof of settlement for has now been handed over to another firm. I have since sent emails and called your firm over 6 times in the past 48 hours to resolve this. At one point I was assured that the collections department manager would call me back in 3 minutes. It is been over 24 hours and still no call. The only thing I am left to assume is that you have *******ly sold off my account to another firm and are now avoiding me. Which is not only ******* but is both ethically and morally *******. Qualities that are paramount for any legal firm. I need this matter resolved ASAP before I escalate it with Council of Debt Collectors and the Credit Ombud.