Just being lied to

After a year of paying more than 60 euros for being without internet most of the time I decided to downgrade. I called 078505050 which is obviously an external call centre. I asked for information but the person would give me the fancy offer names. I insisted and he managed to give me the speed but couldn't understand monthly consumption. It wasn't a language issue he had no idea about the term. Eventually he confirmed more than once, even a bit annoyed, that it is unlimited and after me wanting reassurance that he understood he even said that yes, it stays the same you have now which is unlimited. Lo and behold today I discover that I actually have 100 GB per month!!!! I am trying to cancel and change provider but they guide me through the same number. Is there another number? Even better can I do it simply with the switch number?