I have applied for a UK transit Visa, which is still under processing. Meanwhile my travel date is within 3 days… Will there be an issue If I change the air tickets and hotel bookings (since I did not receive my passport or visa)? How to update the consulate about the new dates?
You applied for a UK transit visa and while it is in processing, your travel dates have changed. You didn't say whether you are applying through a VFS (Visa Facilitation Service) or their internet site, and you didn't say which British consulate you applied to.
In the first instance you should fax a letter to the consulate with the subject "Change of Circumstances" and include your reference number, passport number, and the date of application (best is the date the payment was collected from your account). They may be able to apply a variation for you. If the dates have changed dramatically or your explanation doesn't flush, you will need to reapply.
Send a copy of your letter to them via email. Once all of this has been done, you can then see if their web chat is of any use.