Frankly, it sounds like those complainers are being absolutely ridiculous. It's one thing if you plan on abandoning the game and let it run out of time on purpose instead of resigning -- but if you taking your time making moves in a 45|45 game, then good for you! That's what you're supposed to do!
And I think you're reaction is perfect: be polite and just say "I'm a beginner and so it takes me time to think, that's why I picked 45|45 to play".
And I'd be happy to play you in a 45/45 game!
Your entitled to use your time, maybe disable chat so you don't get bothered in games.
https://support.chess.com/article/209-how-do-i-report-someone
If people get abusive etc report them, otherwise enjoy your chess and use your time 😁.
I don't get that often because I tend to move quickly, but these players don't have any right to rush you into making a move. Especially in a long game like a 45|45.
Some opponents I get are requesting me to play faster
I politely refuse and mentioning it is 45 | 45 and I am still an beginner and take the time to think
Some of them are eventually resigning (usually from a small inferior position) but it makes it really hard to improve since I barely made few moves.
My questions:
1. Am I doing something wrong ?
2. Is it a rate issue, meaning better player are aware of the fact that opponent might take his time and think ?