canon 107 par 1: Both through domicile and through quasi-domicile everyone one acquires his or her own parish priest and Ordinary.
In ecclesiastical law a Catholic person’s bishop and priest is determined by the location of one’s residence or domicile. For example, if you live within the boundaries of the diocese of Steubenville then your bishop is Jeffrey Monforton, he is your Ordinary (consider how many people from Weirton, another diocese and province, erroneously think they belong to St. Peters or Holy Family in Steubenville) . In your diocese you will find a grouping of parochial territories in which certain parish priests enjoy special jurisdiction in their respective territories. If you live within the territory of a particular parish, then that is your parish and your parish priest.
It does not matter if you did not “sign up” for envelopes. It does not matter if you “like” him. It does not matter if other priests tell you that the law has changed. If they tell you that then they are giving you incorrect information.
If your parish priest is unkind or unjust then you must approach your bishop. The presumption is that he has already heard the complaints and has either decided to tolerate the problem, or does not see a problem. What you end up with is not a problem with the priest, but rather, the bishop. He allows the issues to perdure.
A parishioner has more of a claim to a parish than a parish priest does. A parish priest is assigned there via administrative law whereas the parishioner is there by virtue of constitutive law. Priests do not enjoy the former “benefice” model in which they had a right to tenure and income. No, now they are to be transferred at the discretion of their Ordinary.
Now back to the domicile issue. If one has more than one domicile, then the domicile where one sleeps is the domicile that would determine the proper parish and/or bishop (if in another diocese).
What if one sleeps in more than one domicile? Then the domicile where one sleeps the most would determine one’s parish and/or diocese/bishop.
What if your domicile is on the line of the boundary of two parochial territories? Then the direction in which your “front door” is facing would determine the correct territory.