You're not outdamaging his healing. Probably got someone on your team healing, which makes him heal too.

UDK's natural enemy is Rhonda. Rhonda shuts him down quite easily.

Have Ronda, only healer is my ultimate.  Is my UDK healing him?

your UDK heals are going to cause the other UDK to heal unless block passive/heal is up. 

Same here I have a 20 min vid with enemy's UDK at 0% HP. I have UDK , Ronda and Deliana all at full Hp they actually debuff enemy UDK take up that does not exist and after I quit the match the damage is not displayed 

If you are having serious problems with UDK avoid any battles where he is on the enemy team.  Until you can build a team that can beat him.  

Show me your arena team, champion builds, and roster. We can make it work or at least point you in the right direction. 

That's like 90% of teams at lower leagues.   Not an option. 

No offense but alot of these older players have a skewed perspective of the constraints we are working with as newer players.  

If you can get Rhonda maxxed, she's not bad.  But that's a lot of resources for someone new who needs to build up PvE oriented stuff too.  Even still, she is magic affinity.  

For me, it was about blessings.  My team comp is the very easily farmable: (diabolist then high khatun, elhain my starter and farmer, warmaiden and spirit host).  When elhain got her blessings, it cracked the UDKs. When warmaiden got hers, even easier. It went from losing 70% vs UDK to winning 90%.  

The other thing was getting masteries.  I spent my gems on elhain to get helmsmasher and it was totally worth it. Some say you should buy your starters masteries anyway, to get that jumpstart. Wish I listened to them earlier.  

I only play about 10% of Classic arena battles.  I am Gold 5 by being selective.  You cant beat every team out there.