But it isn't thwarting democracy! That's the fundamental error you're making. It's the other way round: democracy is in fact thwarted when a decision that is made is treated as irreversible, when in fact it is not, never has been, and never will be part of democracy to insist on such restrictions. One may as well insist that the last three years, when the intention of 2016 has had to confront reality, are an irrelevance.
The only way (morally, if not legally) to overturn the 2016 referendum, in any case, is a further referendum. If that does take place, then one of two results happens: the result of 2016 is reaffirmed, or it is overturned. But in either case that will only have been possible because the people will have been asked, democratically, to vote on it a second time. And, again, in either case, it cannot possibly be seen as thwarting democracy to have more democracy. I can state it in so many ways but it amounts to the same thing: the electorate today cannot be trapped by the electorate of yesterday. Every attempt to do so in history has always failed, because of course it must.