While I'm sympathetic, I still can't help wondering, why you are asking someone out (or for their number) who hasn't given you a clear indication that they have some interest. If you are chatting someone up and they aren't radiating reciprocated interest, of course you are going to get rejected. You have to develop rapport with someone first, and if that mutual rapport and spark isn't there, then you are just asking for heartache to pursue them in any way.

If you don't know what the signals are that someone welcomes and reciprocates your interest, then it might be good to learn them.