To avoid having it turn your limited no. of equal signs (=============) into a full double line border, if it does this, it usually brings up an icon with a lightning bolt symbol. Click this symbol and deselect the Automatically create border lines (paraphrase). It should then stop doing that for this and all other documents you work on that day.
To delete existing double-line borders, highlight the text that has the borders, go to Page Layout, Page Borders and select None, OK
Sometimes it works to use the Format Painter to copy from a paragraph that doesn’t have the borders to the one that shows the border.