Personally IMO if you want to avoid conflict or getting sued for keeping their money while refusing service than YES you need to make it CLEAR that they will also loose their deposit for the reason

Basically I would just add
Forfeit of the security deposit and immediate termination of service will occur if any of the following behaviors occur:
I also have a clause in my contract that basically states 'the decison of the provider to waive any policy in once circumstance does not negate it in future circumstances'!

AKA I might bend the rules for you ONCE if I feel you deserve a second chance but behave like an ass again and the hammer will come down ~ so for example it sounds like you waived your 'late fee' for them the first times and then got fed up and by their rudeness it sounds like they than expected you to keep waiving the late fee cause they were 'special' or something and are now pissed that you are not letting them be special ~ so whenever I waive a policy for a client I always state 'I am waiving the late fee because this was your first offense but please remember that if there is a next time you will be charged $X a day for each day it is late and if there are continued issues with payment termination of the contract will occur' so they've been warned I was NICE but you screw with me and NOT NICE REGGIO comes a calling cause I will not allow you to behave like this