Really bad hair experience !

Hi there ! Ok, im at my wits end with a problem, situation ive been trying to deal with now for a couple of weeks, i have long hair, never had any problems or issues until recently., To make a long story short, ive developed this matted knot from hell in the back of my head and i have tried just about everything to help release the knot, If anyone has any suggestions or advise i could really use it, Thank you, and i am very grateful !