Never know where you end up

Okay so I have been told this many times, be cordial with everyone, you never know whom you may end up working later in life.

I'm 100% OK with being cordial, but OK with being treated like a footmat everytime someone needs anything

End up not responding, not having the network especially when you need it

How to get out of this loop?

P.S. Strictly professional terms, not personal. Never be friends with ex