I want to cancel my contract

Guys I got the installation but then the services are very poor, it has been installed on the 10th of this month and the services were running for 2-3 days and off again I reported this from the day it went off tell today I am launching a complaint and nothing is happening all they do is send an invoice that I must pay a certain amount... For what!!? They keep on sending reference numbers every day and night but nothing is happening regarding the services I app**** for... ??????