Here's your question (corrected slightly):
'I would like to know who pronounces 'twenty' without the T, why you pronounce it like that and what the official way is'.
And here are some answers:
1. A lot of people drop the 't' sound in their speech, in various different accents in most English-speaking countries. In the US, many people say something that sounds like 'twenny'. In the UK, especially in London, many people put a 'glottal stop' in the middle of the word and say something like 'twen-y'.
2. They pronounce it this way because that's the way their friends, classmates and workmates talk. It's a lazy, sloppy pronunciation, but it's very widespread, and everyone wants to fit in, don't they?
3. The official way is with the 't' pronounced. You should take Dan Smith's advice above, and learn to speak correctly.