Nightmare client - how would you end this

[Sianholby]

So in a nutshell, I took on a new client about 3 months ago and they are a nightmare to work with. Another client recommended me so I thought, why not. For background I am a freelance Project Manager.
This new client micromanages like I’m a new starter, conference calls for everything despite me being in my industry and profession for over 25 years.
They are the least paying client but taking up most of my time, call after call, amendment after amendment, rewrite after rewrite, changing plans last minute and to top it off they are late payers - still haven’t been paid for a presentation I wrote for them in April and May.
My feeling is to dump them as they are draining my time and I’m starting to neglect my other long term clients as this company seems to think they are priority. Is it worth it, they never pay on time, the company are disorganised and overbearing.
What would you do - end the working relationship?

Definitely dump them.

You need to be paid up to date. They have not paid you yet for work undertaken
You don't need this negative impacting client
They are highly unlikely to change the way they operate
They are taking up too much of your time which is not reflected in your fee
They are impacting upon your other clients and work that is profitable

There are no positives here, only negatives.

Definitely get rid, they are taking the piss and likely know it. But to ensure you dont get in this predicament again I would reassess your pricing model. A flat fee is fine but needs to be clarified - this fee covers 20 hours of work which is based on how long this type of project typically takes with my clients. Once you go over the 20 hours, you will be charged my hourly rate.

The unpaid invoices are sunken costs. Terminate your retainer for late payment and move on. The only risk I imagine is public complaint and negative feedback. If that's a concern, be more magnanimous about it. Say you think it is best for you to exit the project at this point for personal reasons, but you don't have share it with them. That personal reason is that you don't like them of course! I feel your pain, I've spent the last week bending over backwards for a client, only for them to reverse ferret on a decision with cost impacts and then lash out in all directions to apportion blame away from their own poor decision making. TBH, I'm glad the engagement can to an abrupt end, even if there is now some argy bargy over the invoicing.

Totally get rid - what's the point of working for yourself if you still have to put up with arseholes. It feels great saying no.

I’d just quit by being too busy for further work. Once they settle your invoices, be blunt if they ever ask again

This isn't working for you. Sack them.

Surely the lack of payment on its own should be enough grounds to terminate?

Get your payments first then end it!

If they are late with a payment then stop doing any work for them. Once paid then do the minimum to get the job over the line. If they ask you to take on a future project then up your price.