There is another method of removing the old text instead of overwriting with the background-colored rectangle.
When you write the value to the screen, save that value in a variable for future use.
When it is time to write a new value to the screen, write the previous value to the screen with the text color set to the background color (this effectively erases the old text), then reposition the cursor and write the new value to the screen using the actual text color.
You should already be saving the previous value written to the screen, so that you can compare it with the current value and only rewrite the display when the data changes.