Your inquiry regarding the difference between C-18 and D-18 in ESIC Delhi.
First of all, it is the same all over India. C-18 is a notice proposing to determine and recover contributions in cases of defaults/omissions. C-18 Interest is a notice for payment of interest on delays in remittance of contributions.
Now, coming to D-18, it is meant for the recovery of damages on delays in remittance of contributions. In cases of C-18 (ADHOC) and D-18, the ESIC shall afford a date for a personal hearing. You can approach on the date and time specified and represent your case.