Gold Car Complete rip off

We use budget car hire firms extensively and often for long periods.
Gold Car are the worst by a good margin.
We have our own insurance so don't need the very expensive extra insurance they offer.
In this situation most hire firms will require to 'block' around £1000 on your credit card in case you trash their car. This is fine and normal but Gold Car actually TAKE the money and a apply a very high charge on the euro conversion. Assuming all is well they will then return the deposit but again using a very high charge on the exchange rate. on our last trip their charges were almost £100.
The first time Gold car did this they said it was because I used a debit card rather than a credit card, this was untrue as I used my Visa Credit card.
On our last trip I checked this situation before booking and read that Gold Car would NOT actually TAKE the money from my credit card ( but just put a block on it) When we collected the car the money was again TAKEN. We complained and were told that it was because we had booked through an agent. We will NOT use Gold Car again.