| This has been known for a long time. Stewball is an old traditional English folk song that doesn't have a copyright. Here is a link to the story of the creation of "Happy Xmas" "
There are many songs in the history of rock n roll that use melodies from earlier non copyrighted songs -
Whiter Shade of Pale
House of the Rising Sun
Girl From the North Country
| in the first verse. Can't listen to the whole thing right now but I will.
Sounds very nice - you have a right to be proud.