Car rental final invoice problem

I am a spanish citizien resident in the UK. I booked a car from the Italian company Ecovia for my Christmas holiday at Italy.
The 2nd of January we went to Ecovia offices at Florence City centre to pick up our car. At the collection desk we were asked if we wanted to pay for a damage and theft excess insurance. They told us that we had two options: we could pay the maximum deposit and don't pay for any insurance or we could pay the insurance and hence the deposit amount would be reduced. The value of the insurance was too high in our opinion and we had another insurance so we decided not to pay for it. We told them that we didn't want the insurance and prefer to pay for the deposit of 1400€. We checked the contract and in fact the deposit was included and we paid with our credit card this amount. No further payments were done at the collection desk (we have the card recipe of the deposit). The trip passed without any problem an the 6th of January we returned the car at Pisa airport's Ecovia Offices. They looked for any possible damage caused to the car and if the fuel was full and everything was ok, so we didn't pay anything extra.
The 7th of January, the day after we returned the car, left Italy and arrived back to the UK, we were charged 149 pound plus a non-sterling transaction feed at our credit card from Ecovia. We contacted them asking if was a double payment of the car rental (since the amount was very similar to the rental price). They answered us telling that this was not a double payment but a payment of the one-way fee and the full cover insurance and provided an invoce. We are totally agree with the one-way fee, since we know we had to pay for it from the beginning of the booking process but we are not agree with the insurance charge. We told them at the collection desk that we didn't want the insurance, however the insurance is included in the contract and we didn't realised about it (the contract is confusing and when we saw the deposit of 1400€ we considered that everything was ok and I signed it -a big mistake, I know-). We contacted them again telling that we didn't order the insurance and that we wanted a refund but they do not answer any longer to our e-mails. We don't know if they included the insurance on the contract by mistake -it's strange to have in the contract the maximum deposit of 1400€ and the insurance at the same time (¿does this contradiction invalidates the contract?)- or if they just wanted to fool us -¿is it legal to have been charged for an insurance after finishing the period of coverage? and ¿why have we not receive any information about the insurance at the collection desk?-.
I would appreciate any advice about how can we solve this complain.
Thanks in advance for your time
Omar, da Lincoln (EE)