Sometimes, ATC does things that you are not happy with. It may “forget” to give you vectors or descent instructions; it may get choked up if too many AI aircraft are in the vicinity; it may get confused by a buggy airport… Conversely, sometimes ATC is quite correct, but you did something wrong with your flight plan, or did not read back, or did your own thing, or maybe you were “naughty” and got warned too many times: “Don’t transmit when the channel’s busy”.
To fix a sulky ATC, try asking for flight-following (if ATC will listen to you) and then canceling the flight-following service. Then, file a new plan (while in flight) and ask ATC for clearance. Hopefully, ATC will then behave itself.
Please remember that simulated ATC, in contrast to a real human controller (IRL or on Vatsim), is a mind-blowingly complex piece of programming. X-Plane’s ATC system is constantly undergoing big changes and improvements, so what does not work so well now may well work brilliantly after a few update cycles. If you compare ATC in the last version of X-Plane 11 with that of X-Plane 12 (current version), you will be amazed at the improvements.