The Iron had led since the 22nd minute through Sam Winnall's goal before Sampson's late header held them to a 1-1 draw which prevented them moving four points clear at the top of the table.
Wilcox saw his side extend their unbeaten run to 27 games but was furious that his team did not hold on for the three points.
He said: "The referee gave six minutes of injury time and I have no idea where he got that from at all.
"There were no major hold ups at all and I'm just in a bit of shock. When they saw the number six go up they had a real lift as you can imagine and the crowd got right behind them as well.
"You have to give Morecambe credit for the way they showed great spirit but as much as I am annoyed about the added time I'm also annoyed that we didn't hang on.
"We have let a lot of late points slip this season and it is a bit embarrassing I have to admit now. We have taken the lead in 29 games this season which is incredible really but it makes it all the more disappointing when you lose the lead so often."