Which day is the 7th day of the week?

SO which day is the seventh day of the week as the calendar has changed so many times over
the centuries since the Law was handed down to Moses on Mt Sanai.
The calendar that we use today was instituted by Pope Gregory X111 in 1582 AD replacing the Julian calendar used since 45 BC.
The Gregorian calendar that we are using today actually shifted the week by 10 days so the Sabbath day that was observed in the Julian calendar has now been shifted by 10 days and no longer falls on the same day.
Closer to home, in Samoa when the date line was shifted just a few years back to the East, Saturday has now become Sunday so Sabbath worshippers in Samoa are now actually worshipping Sabbath on a Sunday!!
How weird and irrelevant this observant of the particular day has become.
This argument of the Sabbath is not new and was a contentious issue between Jesus and the teachers of the Law when Jesus was
accused of not observing the Sabbath.
Jesus said in Mathew 12:8 that the “Son of Man is Lord of the Sabbath”.
He even went on to say when asked what is the greatest commandment in Mathew 36-40 that “Love the Lord your God with all your heart and with all your soul and with all your mind” this the greatest commandment and second “Love your neighbour as you love yourself”.
He did not say and the Sabbath.
So why argue about the Law when we should all be seeking his Salvation by accepting that he is Christ, the Saviour and NOT by observing Sabbath.
So which day is the Sabbath again?  I am in Samoa!

Accepting Christ