Your demat account is always 16 digits. In case of CDSL depository account all 16 digits are number.
In case of NDSL depository account first 2 digits are Alpha and next 14 digits are number. ProStocks is Depository Participant of CDSL.
DP ID stands for Depository Participant ID, first 8 digit of you demat account identifies your demat service provider called Depository Participant and in short DP ID (similar to IFSC code of your bank account)
BENEFICIARY ID = 8 digit number that identifies your individual demat account number with your demat service provider.
Combination of 16 digits = DP ID + BENEFICIARY ID = your unique demat ID. (This 16 digit number is sometimes referred as beneficiary ID, while filling up online IPO applications)
You Unique Beneficiary ID remains the same, as long as you maintain your demat account with the same Demat service provider.
Your ProStocks CDSL Beneficiary Demat Account Number always begins with '12083200'.