I must pay for there mistake

I use Jenny internet as a service provider, They did a remove and re install of my internet and half of the work is done. the cables is not neatly done and i struggle with my speeds. This is from the start i struggle and complain but noting is done. Now the saw there is a a problem with my speed now they want to charge me for there mistake. How is this possible they do not do the work correctly and now i must pay because it is not done correctly from start. And my Invoice is paid every month on time. I am Fed up.