When you say a complete and utter lie, I do believe there is still a sizable net amount that is in the EU favour? A quick google suggests £120 Million - £188 Million..
The £350 Million is the gross amount, which was disingenuous but it's almost as if people think that the £350 million had absolutely no basis at all.
To say that £350M was under control by the EU wouldn't have been THAT bad, because it is the cost of the liability.
However that's not what was said, the £350M is how much would be saved, which could be given to the NHS in the event of brexit.
Because we don't spent £350M in the first place, there's no mathematical possibility of making that saving, so it was a lie - and so the claim being made in the first place, has no basis.