I love my Olfa mat, but I had a cheapy Dritz mat before that which lasted me until a family member had the "thoughtful" idea to store my mat upright while I was in the hospital. Came home to a wavy, crocked mat. I was able to revitalize the mat for a while by soaking it in the bathtub & giving it a gentle scrub with a sponge and Dawn.
That said, mats do not last forever & if different rotary cutters & new blades don't solve the problem, your issue is almost certainly with the mat.