With the recent Service Charge update, L&Q amended the Direct Debit settings. Everyone should receive an email about this change. Ensure the amount in the letter is the same as what you have in the Revised Service Charge letter. If you have different amounts in those letters, call the L&Q Direct Debit department and ask them to fix the issue!
In my DD letter, the amount was £30 higher than the revised total amount.
L&Q Direct Debit contact number: 0300 456 9996 (ext. #2 and then #1)