He gave you the formal definition of heresy as held by both Orthodox and Catholics. You respond with Webster's definition. Do you know anything about language? Websters and all other general dictionaries merely seek to report the common usage for a word. As usage changes, new editions reflect it. The definition you give reflects common usage of the word heretic.
The definition Bohemund posted is the definition the Church has always used. Even Presbyterians and Episcopalians use it when they put someone on trial for heresy, e.g, Charles Finney in the 1800s and more recently, some Episcopalian wackos.
The key element in defining heresy theologically is that it must be a really chosen error in biblical interpretation (in theology). The Greek word simply means choice. To make a real choice one must first have knowledge of the various choices. So no one can be an unwitting heretic. The second major element is that one must persist in this knowing choice. That's why heretics (those making erroneous doctrinal choices knowingly) are first formally put on notice that their beliefs are erroneous. Only if they do not change their position are they heretics because at that point they are pertinacious.
You meet the second criterion (pertinacity) but not the first. Not because you have not been put on notice but because you seem to be incapable of understanding relatively simple reasoning.
Heresy is in the eye of the beholder. Your church defines it in a way that favors its interpretation and everyone else defines it according to their beleif. You think your position is the right one and we are heretics and I happen to think you and your's are heretics. So who is right, only God knows. But this I do know, there will be no excuse at the judgment seat "but that is what the church taught".