Delayed tactics at Credit Bureaus

I sent in a paid up Letter on the 26th of August 2020 to dispute a default on my Credit Report. It has been 2 months now and still it is not taken off my Report and NO changes affected my score. I have sent lots of emails to have an answer to two ladies who are in managerial positions but they do not meet my need. Two or three of their responses just say that they are busy investigating. Yesterday again I send in another request but zaconsumer's response is they received my request this will take up to 5-21 days and so the whole process start again. Can't they pick up on their system that my ID has been investigated. The other problem is that the Credit Bureaus recommend that to increase your score you have to have credit that you pay but I cannot open any account because of either my score being too low or the fact that I still have this reflecting on my name. Everytime I apply for even a small account it is declined and then reflects as a credit enquiry. Please help