Faulty on Rio kia

Ive had my kia rio for 6 years and never had issue with service or quality up until now.. I took my car in to kia in centurion for service and for them to have a look at what I firmly belive is faulty on kia side.. on my right back door the rubber on edging of the door has completely melted onto my door.. when ever someone opens my door its left with sticky black stuff on my car causing damage on my paint of car .. Kia centurion has informed me that its my problem and I need to pay over R2000 for them to repair whole rubber on the door.... this is ridiculous as I do not understand why this rubber is just melting.. never in my life have I seen this with in other car until now...

To have kia tell me straight up that I need to repair it .....