GoldCar Rental review: Car hire - forced additional insurance purchase

I had pre-booked and pre-paid for a Goldcar (owned by Europcar) vehicle, and upon arrival at the airport I went to sign the paperwork to collect the car, where I was effectively forced to take out and pay for additional insurance that I did not need nor want due to an alleged Goldcar policy that had not been advised to me in advance of the rental collection, and similarly has not been demonstrated to me as an existing and published set of rules since I have made the complaint.
At first I declined the offered "Super Relax coverage" and showed the Goldcar operative, that I already had additional insurance. This being so' I advised I would (which was a valid and advised alternative) leave the optional deposit by way of a "blocking" transaction on my credit card.
However, despite my credit card having my name on it, as required by the terms on the rental agreement, I was told that as my first name only appeared as an initial on the credit card rather than my full name, they did not believe or accept that the credit card could be mine, as per Goldcar policy, and so my only option was to pay the additional fee (or lose the amount that I had already paid for the rental and seek a last minute booking at the airport with another rental company, for an additional amount). I asked the operative to show me specific naming requirements regarding the credit card policy on the rental agreement and the operative could only show me where it said a credit card in my name, which I had already presented. I showed the operative all of my other credit and bank cards, all of which have my first name initials only, and pointed out that in all my years of credit card transactions overseas that there has never been such an issue, but the operative did not accept this. During this conversation your operative was in possession of my passport and photo ID driving licence yet my identity was somehow still an issue. The first reply I had from Goldcar after my complaint did not directly answer my contentions, and simply suggested that "In this case and according to the information provided by the rental office, the security deposit could not be blocked for the requested amount." When, in my response to this, I advised that there had been no attempt to charge my credit card, the further response I received from Goldcar was that I had signed the paperwork and I was to note "that purchasing this coverage is completely optional. If you choose to accept it when picking up the vehicle, it means you agree to it."
My latest correspondence, in reply to this, which remains unanswered except for a refusal to further communicate, was: "In reply to your email I can confirm that the two options that I had were either (1) pay the additional amount for the Supa/Mega Relax coverage and sign the agreement or (2) not pay for the Supa/Mega Relax coverage and seek an alternative rental company whilst losing the rental amount I had already paid for the car. Your operative put me in this position of having to agree to it, by refusing to take a deposit on my valid credit card, the excuse being that my full first name was not on the credit card. My dissatisfaction remains and I do not see the situation as being resolved." I have since discovered on social media sites, that I am not alone in having received this unjust and unsubstantiated treatment.
In summary, my contention is that I have been subject to:
1) forced purchase of unwanted insurance based on rules that were verbally advised to me at point of purchase but are not published or discoverable,
2) non-response to my specific, detailed and substantiated complaints.