The state of his bedroom driving me mad

[Quiegal]

My son 15 ADHD just driving me completely crazy how his room is always in a mess. He says it's tidy when it's really not.
Yesterday walked in their told him open the window it smells like a dog been in here.
I have helped him several times but this issue just getting worse and worse.
Recently he caused a big argument with my dad because of it.
My partner and I have done our absolute best telling him clean your room. Helped him several times it just goes back to mess after a week.

Any suggestions please

@@Beamur

@Theoldwoman

Thanks I will try this. So many good things people have suggested to do.

I said to him he needs to do bedroom tommorow. I knew he wouldn't do anything when I went to work.

Just about got him washing his school clothes. Telling he needs to do the shirts.

I even told him he needs to shower hasn't listened. His hygiene bad too.
Will not wash or shower whole weekend you have to keep going on at him.
Constant battle.

Sorry my phone playing up today..