Hertz - Security deposit taken, not returned

Let me have a little vent.
Here's an overview:

I rented a car from Hertz via Ryanair in the UK in late March. The quote from Hertz was 50 euros for the three days. Great value for money, I thought...
The 50 euros was deducted from my CC at the time of booking.

On the day of collection, they were having some issues with their IT system so as far as I recall, they processed the security deposit of 300 euros manually and all seemed well.
Let me add, I have never have had a problem with Hertz previously so off we went, did our thing and returned the car on time, with a full tank of fuel.

Anyhow, fast-forward to May when I checked my statements from March (yes, I left it a few weeks) and lo-and-behold I see a charge for 50 euros and also 300 euros on my card, with no credit for the 300 euros. I checked my gmail to see if I received any notification of the deduction - but no email found from Hertz.

So mid May, I sent a polite email to Hertz Ireland asking for them to look into it.
The responded within 48 hours to say that the rental was handled by Hertz UK and that they have passed the complaint onto hertz UK and that I should expect an update within 14 days.
...well, I'm a nice guy and I'm patient too, so I waited... 14 days. I sent a follow-up on the 15th day... no response... I sent a follow-up on the 21st day.... and again no response...

So I'm at a juncture... I'm filling in my banks ChargeBack form as I have given Hertz ample opportunity to rectify this. But, typical of the banks, they have a 'very strict' rule about not processing chargebacks outside of 60 days from the statement date.
Well... when it comes to banks, nothing would surprise me...

Anybody have an email address for hertz's complaints department???