Hi, I'm Carl and welcome to Just Answer. What color toner is on the Transfer Belt? If you've replaced the Imaging Units, Transfer Belt, and Roller the only other thing that can leave lines are the Drums. Depending on which color Toner it is, that will be the Drum you will need to replace. Hopefully it hasn't scored the new Transfer Belt or you will have to replaced the Drum along with the Transfer Belt again.
If you need any clarification with this or additional help, please don't hesitate to ask me.