Real Bump/dump groups need liquidity and not a specific number. if group users are 1000 and the investment value is $ 100, it is only 10 requests from ordinary people or one request from a whale, so all the groups looking for subscriptions from customers are scam.
The only groups that may create an effect that have liquidity and then they will not ask the users for money, but rather the users will lose their money with each pumping and dumping.
In general, it is a risky activity, the cryptocurrency market is in an upward stage and with a little effort, you can make profits instead of such an investment.
Sorry for your lose.