JET Stores/ Nimble is busy causing problems

They are the worst company out there. The have new ownership called Nimble, but there admin department never closed the old account on credit score, so my score is so bad due to both accounts showing active and overdue. And on that they cannot see my payments reflecting, so I don't know where my money is going every month. I have emails where they said that it is their fault for the credit score, so I asked a letter over two months ago and not received it back, but they still phone for payments everyday. I tried to explain to them today again that it is a mistake on their side and the lady laughed at me so hard over the phone, that I was not able to complete my sentences. Their service is the actual joke.