Bogus charges

We booked a car via Expedia.com from Enterprise in the US for pick up in Rome, Italy.  When we got to Rome Airport we found that Enterprise is operated by Locauto Car Rental.  On checking in at the Locauto desk, we were told that we have to supply two credit cards which has never been a requirement with any other car rental company we have used.  In retrospect we should have realized that this was a red flag.  They then handed us a GPS which we said we did not want as we have our own TomTom.  The check in person said that we have to take the GPS as it was compulsary and that we should just leave it in the car.  Another red flag that we missed.  Two weeks later we returned the car to Rome Airport where a group of 4 or 5 people descended upon the car looking for damage.  They did not find any and when we went into the Locauto car return office to get our paperwork, we were told that there was a disk missing from the GPS.  We informed them that we at no time had even opened up the GPS and we were returning it in exactly the same condition as it was given to us.  We wrote out a declaration on the return documentation telling them that we in no way were taking responsiblity for this so called missing disk.  This is obviously another Locauto scam in case they can't get you on scratches, windshield or any other made up infraction.  A week after our return from Italy, we received an E-Mail saying we have been charged an additional 550 euros for the missing disk.  We left numerous messages on the Locauto Customer Service site but they did not seem to even read them and just kept replying that we still owe 550 euros for the missing disk.  We fought the charge through Mastercard and they reached out to Locauto and asked them to supply additional proof and documentation to support the claim and none was forthcoming.  Mastercard eventually credited us back the 550 euros and told us that they consider our dispute resolved.   Last week we received a letter from a collection agency in Italy, threatening that if we did not pay them 699.92 euros (the addional charges being for what they call interest and fees) within 10 days that they will start proceedings against us in our own country.  These people are reprehensible and MUST be stopped.  We would like to pursue a Class Action Lawsuit against Locauto and Enterprise and would be pleased to hear from anyone who would like to join us.