Different deal not specified by sales person

Unfortunately their sales people are so quick to sell you a fibre package, that they forget to tell you if you change the fibre provider to another company, the terms with which you initially signed up a month ago, with the other provider, will no longer be valid i.e. first 2 months free when signed up in Oct 2019. Called and called to find out about installation of fibre, and was told that another fibre provider have taken the lead with installations, and that you can change to that other fibre provider. When you do so in Nov 2019, they do not tell you the special was only until end of Oct, and you only get the surprise of a debit order going off your account the day your fibre goes live. I think the sales person was supposed to look at your deal you signed up for, and advised that the 2 first months free is no longer applicable, before you decide to just change the provider to another one.