Call the hotline to report your concern, change of plan should not affect the phone in the first place since the change is for DSL connection. You can use your Globe Mobile to call the hotline by dialing 211.
Several factors can be reasons for this.. like what numbers you are trying to call? local? other networks?
else better call Hotline for that using any gloibe mobile 211, for deeper account checking. juneevans give us update on this please once there's any changes.