No follow up on queries for extra charges

I traveled to Aberdeen, UK on 18 June this year and hired a car through Avis . They took my card details as is standard and paid the deposit. I returned the vehicle 7 days later, 24 June, as was the deal with a full take of petrol. At the drop off, the Avis employee checked the vehicle and said all was good and I left. On 20 July, my card was charged GBP30, and then again on 7 August. I went to the Avis-Europe website, on the 7 August, and sent them an email asking what this was. I got an automated response with a reference number and was told it would be responded to within 15 days....HA! I sent them ANOTHER email on 31 August... Still no response! I find it shocking that after over a month, this world wide company doesn't bother taking it's customers seriously. We just pay your bills and salary's.. There are plenty of other car hire companies out there who would prefer my business.. I wait with abated breath.. Hoping for a miracle...