Hello student,
According to university grand commission or UGC a diploma degree can be off total 3 years or 2 years program . In very few cases there are few programs which are one year diploma degree. WhatsApp to say you I never heard of 4 years long diploma degree course. If you are talking about that you got suplee in the examination and you have completed all of your backlogs in  total of 4 years. Then I can say that the degree will be equivalent to your original diploma degree don't worry.