Um, if you asked somebody in my country (Czech Republic) for phone number after chatting with them for a bit in a Mall, they'd sent you to hell.

I often chat with people on happenings, or when we are together on some long bus or train ride and such. Yeah, sometimes we exchange numbers, but I never replied really. Why? We had nothing in common, except being at the same place at the same time.

Employees probably get asked for numbers a lot. Maybe they wanted to try it out, if they have something in common with you........ the spark wasn't there. Would you continue to text with somebody whom are you not interested in, just not to hurt their feelings? You know how exhausting it would if everybody had to keep in contact with everybody they ever met and gave their numbers to?

Don't go blaming your mental illness. It has nothing to do with this. You not isolating. You have trouble approaching people. But as others said, do it in places where you are more likely to meet people like you.