Cattleya with White Bugs on Roots

[Tindomul]

It sounds to me like you had some springtails. Harmless insects that were probably eating dead or decomposing organic material in your pot. When you repotted, were some of your roots dead? If so, thats probably what they were eating. Or the potting material that was tired. In which case you can thank them for eating the rotting material before harmful fungus and bacteria had a chance to do it.
Most pests don't run around the way you described it. They stick to the roots and leaves for dear life not matter what you do.
So I think the culprit was something else, perhaps you were keeping too wet or it was too wet from where you bought it. Re-potting it may have been what saved it.