Just keep grinding games, the more you play the more accurate bracket you will be in. The low tiers tend to be filled with a lot of ignorance and anger. Once you start getting matched with people of equal skill then you will at least have people who are learning the game around the level that you are. Venomancer is a fine hero, especially if you are new to the game. Though there are plenty of times in which he is an awful choice. Maybe your team doesn't have a carry or any sort of inititation, don't last pick him because he doesn't fill those roles. I would suggest sticking to the set of easier heros and focus on your personal learning rather then getting bogged down with team compositions. Just ignore the flamers and try to figure out what you did wrong and how you can correct it in the next game that you play.
As soon as you make it beyond that 1st pool, then you get into the pool of "Hey we need wards!!!!", people calling gg as soon as the game starts because nobody on the team picked support, and apparently nukers, or anything not hard carries are considered support for some reason.
Support isn't a class or specific set of heros. It is a play style based around the lineup your team / opponents have. Gyrocopter can be considered a support and we see him being ran in that role in a lot of professional games. Most people consider Mirana a Semi Carry, however her best role is that of a support due to her mobility / stun. Vengeful Spirit can be played as a support or as a carry depending on how you are allocating farm and your item choices. Some heros that have burst damage such as Lina or OD can be played as a carry or as a support based on the laning / item progression. It is all about hero synergy and the over arching goal of your team and its current match up that sets up which heros should be allocated the farm. You can't take heros and stick them into nice little groups, there are tons of grey area...which is what makes Dota such a beautiful game.