Why my samsung washer and dryer takes too long to dry?
Maybe the problem is not the dryer but the washer.
Your machine is both washer and dryer and you have thoroughly investigated the dryer.  Maybe your washer is leaving clothes too wet.  I had trouble with my washing machine when it would not spin enough and clothes stayed wet.  They were too wet for the dryer.
Run a load but do not dry them - have it stop after wash cycle.  Are clothes dripping wet?  Sometimes a washer thinks it is unbalanced or for other reasons does not finish the cycle like it should.