Poor customer relations

I moved out from a 1 bedroom flat in which I never missed a payment on any of my bills. I took all the right steps to advise all my utility providers the date I'm vacating the property and if there were any outstanding payments I needed to make before I move andeverything was very professional and straight forward.. until I dealt with UU. The gentleman I spoke to was very polite and informed me I was actually in credit and I'd receive a cheque at my new property. So far brilliant. Cheque arrived and didn't think anything else of it. Almost 2 months after moving, I received a red letter and a letter from their legal reps threatening me with court action. Totally out of the blue!! After long conversations with them, they owned up to an error and dropped it. Although this is resolved, I think it's disgusting how they threaten very good customers who have never missed a payment. In hindsight maybe I should have taken this further but with stresses of moving still adapting to my new home, I let it go. I think this company needs some serious customer relations reflection. Go after the ones who deserve it, not good, honest and reliable customers. It made me sick with anguish. If I could change, I would. They just have the monopoly. Well done UU. You should be ashamed.