When you hold the units in a demat account, the units in your demat account gets allotted in the Demat Account number under the ISIN, the DP does not store the folio number. The RTA in turn assigns the folio number and the details of the folio number are as per the information available with your DP.
When mutual fund holdings are stored in dematerialized (demat) mode, the Registrar and Transfer Agent (RTA) retrieves information from the depository on a weekly basis through a BENPOS file. This BENPOS file compiles various data from the Depository, including phone numbers, email addresses, demat information, and more.
Recently both the RTAs have upgraded there systems to show the data for units in demat mode correctly, more information has been added below
Here, the RTA is liable to grab that modified information for your folio and update that in their DB in all the Demat Maintained folios. So you need to nudge your DP to check with the RTA on if the RTA has been correctly consuming the data or not