I think you will find that the weasel words they use on their contracts will say something like "up to...". I suspect you will waste your time and money in trying to get them to really give you what you think should be due to you! It seems to me that most ISP's use the same terminology and unless you live in the local exchange, I doubt you will get the speeds you anticipate. Unless you are in the Fibre Optics system, which should be somewhat better than copper wire!
There has been many comments on this Forum which relate to similar problems of paying for something and not getting what people think they are paying for. On the other hand, there are people here who do get what they have paid for.
Not an easy problem to sort out!