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The Third Commandment to keep Sunday holy is Divine Law, our obligation to go to Mass is an ecclesiastical law, it is called a Precept of the Church, it is the first of the 6 Precepts of the Church which makes it our obligation to go to Mass under pain of mortal sin, but it is not a Divine Law.

You're making a simple question, complex.  Yes, Mass is part of the Divine Law.  No, its obligation is not simply a church law.  Without Mass, there would be no need for the Church.  Without Christ dying on the Cross, the Church's existence wouldn't be possible, nor would it exist with any purpose.  You're splitting hairs here, and not in a good way.
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How do you "keep Sunday holy", except through worshiping God?  How does one worship God, in the Catholic Faith, except through the Mass?  The only way the Sunday obligation would cease to exist is if the Church's operations ceased (i.e. persecution shuts down chapels, or there are no priests to be found, or you live too far away from a church).  You can't have the Catholic Church without the Mass, and there is no Mass without the Church.
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The obligation to offer sacrifice to God (i.e. Holy Mass, the perfect sacrifice) is a continual theme all throughout the Old Testament and Holy Mass is just a perfect fulfillment of these former offerings.  So, yes, Mass is part of Divine Law.  But it is ALSO part of ecclesiastical law, because the Church wanted to be specific on WHEN and HOW MANY TIMES we had to go to Mass.  The ecclesiastical law is only dealing with the specifics of the already obligatory Divine Law.

Did the name/location of the church ever get revealed?

If not, why not???

Without that, the OP’s claim sounds like BS.

I'm the OP. Yes I did disclose the name/location, and, no, not BS. However, after much discernment, we have arrived at a decision. Thanks in part to the great debate on this forum. And the discussion of both sides of the situation. Thank you everyone for your help.