Hard to cancel once you in, bad internet provider

Really good at selling you a product but really bad at providing the product sold. Had a fibre line from them for a few years, never got the speed I was paying for finally it got so bad I was forced to cancel and get a different internet provider. Gave them many chances to fix issues but no response. Then after canceling they had the audacity of continuing to try to bill me. I actually tried cancelling for many months prior, really hard to get them to stop contract. After a year now with being with another provider, they still trying to get money from me, really shocking. Even after giving them there 2 months notice of cancelation. Seems like there is no correspondence between departments at Vox. Had already forgotten about them and then they had the nerve to put a debt collector on me today for some cancelation charge that I have now been informed of for the first time. So its fine if I pay them for years with not getting what I pay for but if you dare to cancel then they want more money for that to ? Crazy times.