Just updating for information's sake. We eventually got Auto Europe to sort it for us. Amazing how the squeaky wheel gets oiled. We rang them again, got onto a supervisor, explained that we had booked a car with a debit card, it was Friday evening, travelling for business on sunday and could they possibly help us? Well Supervisor got onto Bergamo for us, and arranged that on payment of 500E he could have the car on Sunday evening, as per booking. And on return, he would get full deposit back, barring accident etc of course. Sent him an email to that end immediately. Very helpful in the end, got him totally sorted and a HUGE pressure off him thank god.
Best bit is, when he got to Bergamo, they only asked for 350e, and e got every penny back when he returned the car to Rome. No excess payment, nothing. So its do-able, just not easy.
Credit card application for future use is in process.