"The increasing CPC runs on trend with the declining CTR."
An increasing CPC will not say you are being pulled down to the "lower quality traffic" per se. The combination of lower CTR and over 2 mil views (which is your actual audience size) I guess you burned the audience with the current ads.
Refresh the ads is my suggestion, and try to tackle this faster in future. Discover new angles and find new images while your current campaign is doing profit so you can replace if needed without having to pause or losing volume.
Thanks Stickup...
I thought this was proving too easy, at this rate I'll need to turn creative and angles every 1-2 weeks.
Yeah, originally I was duplicating within same campaign by ad group, but following your responses to other recent posts I've now started duping by campaign too.
There's about half a dozen campaigns live, each with different ages or IOS etc, (screenshot above is just the longest running one) but they have all seen a similar dramatic drop in performance at about the same date.
Either way Ill do some more creative testing and see what I learn.
Thanks 
If you are just refreshing a creative within a campaign (assuming it is setup like this: 1 campaign - 1 ad set - 1 ad), do you just turn off the burned ad set and add a new one within that same campaign, or do you turn off the entire campaign - duplicate - and refresh with a new entire duplicated campaign? Or do you find it doesn't really matter and more of how you are tracking your experiments?
Yes that answers it, thank you!
I'm suffering from the rapidly doubling and tripling CPC too (usually because of doubling or tripling CPM while CTR stays relatively consistent). Most recently I would start my campaigns at $20 budget and then raise to $50 then $100 then $200. By the time I'm at $200 budget (hasn't even been a week) my CPM is already more than double what I started with. It's been so frustrating!!
The question is if scaling really provides you more money at the end. 50 dollar spend with 100 dollar revenue for weeks, or scaling to 200 with a revenue of 350 for some days only. It's really hard to predict and it's quite natural you get greedy after a while of doing xx/xxx a day "only".
In general I try to get the maximum ROI I can get, even if I have some ads doing 100/200% ROI and I see there is still room at CPC side to improve. If you are on thin ice with a 100% ROI at low budget, its very hard to keep it 50% or higher if you start scaling. But if you really optimize ads to 300/400% you know scaling will be much easier with plenty of room to cash even if your cpc will be doubled during the scaling process.
And this Q4 is one of the hardest in years I think. 2017 has shown growth of mediabuyers and agencies putting their budgets on FB traffic more and more. Thereby FB makes it harder for us "black hatters" to run a steady business. Good luck, be patient and optimize as you never optimized before haha!