GoldCar Rental review: Dangerous vehicle supplied

I recently had the misfortune to hire a car from Goldcar for my use during my family holiday to Italy.
I say misfortune because on Friday 19th July, one week after picking up the car, I noticed that the oil light kept flashing on when turning corners.
I checked the oil dipstick, and it registered NO OIL in the car engine. I made numerous telephone calls to various telephone numbers I had for Goldcar and spent nearly an hour on the telephone trying to find out what to do. How much oil to put in the engine, what type of oil, etc. I could not get through to the breakdown service number provided by Goldcar, there was no answer.
I eventually went to a local agricultural mechanic, he put 2.5 litres of oil in the engine, he also added 2 litres of coolant because there was also very little coolant in the system. He checked for oil and water leaks and found none. He also said that looking at the oil filler cap the oil had never been changed in the 86,000 Kms the car has travelled, the deposits on the inside of the cap proved this.
I really found this all very difficult to believe, that I rented a car using Goldcar because I thought they were a reputable company, not realising that the car I hired from them could potentially have had a seized engine whilst travelling at 130kms per hour on an Autostrada leading to a very serious if not fatal accident involving myself and my family,in other words a deathtrap.
When I returned the car on Wednesday 24th July to the rental desk in Pisa airport, I was told that every car is serviced before every rental. This is a lie! This car had never been serviced and no-one has ever checked the oil and the fact that it also needed coolant should tell you that this car had never been serviced in all of its 86,000 Kms.

I asked Goldcar to check their telephone logs to verify what I stated, my telephone number to be found in their records is; +44 (0) *************.

I attached a screenshot of the receipt I received from the mechanic. I realise that this was not on headed notepaper, but it is all I could get from the mechanic I used. Given that I trusted Goldcar to provide me with a safe well maintained vehicle for my holiday, and they failed I expected they would be able to trust me when I told them that the receipt attached was genuine, and I required a refund of €37.50 for the oil used to maintain their vehicle in a safe roadworthy condition. Just for completeness, I gave the mechanic €50 for his service, the extra €12.50 was for his labour, but I had no proof of this.
Goldcar claim they have now refunded me but one month later and there has been no credit to the account I supplied them details of. They have refused to refund the €12.50 labour charge because I did not supply a receipt. They have now stopped replying to my emails and refuse to escalate this complaint to managerial level.
They did not even issue an apology for the appalling service I received nor for putting my life and the lives of my family in such danger, a seized engine travelling at 130kph would have led to a very serious accident at the very least if not a fatal one.