You're welcome - this is a great place to come to for help, ideas, & suggestions! I've only been a member since January, and have received lots of excellent advice from members - they're the best!
I've also used one of those sponges (dry) that has a fine soft scrubbie material on one side, using very light pressure, rubbing back & forth, all in one direction (side to side), wiping with a damp sponge, and then if needed, using the scrubbie side and going over it again in the opposite direction (top to bottom), then damp sponging it as a final step. The key is to go all in one direction - NOT IN CIRCLES - then in the other direction.
Better than nothing, and if it doesn't help, it's time to 'bite the bullet' and get a new mat! They (like so many other things) weren't meant to last a lifetime!