Bad credit score due to Mr Price

I had an account a few years ago and closed it, I recently opened an account with them because I wanted my credit score to increase. I made payments on my account and my credit score decreased due to bad payment, only to find out the payment I made went into my older account. I contacted Mr Price on numerous occasions telephonically to correct the error but not has happened. I recently contacted via email as well to no response. I want the account closed and also I want the funeral cover stop with immediate effect. I had to buy my property end of December but got declined due to my credit decreasing instead of increasing.