Just got back from a BA Holidays Flight + Car package, only to find that Avis have charged my credit card what is presumably the amount agreed between BA and Avis.

The BA rental agreement was 14th Aug 18.00 until 30th Aug 18.20 Group K. Actual pickup time was 14th Aug 20.10 until 30th Aug 17.16 Group K.
I've downloaded the receipt from the Avis website and it is clear that it is the basic package charge that I've been billed US$1,168.03. All other options were declined, but in any case the LDW excess for the US rental was $0, full tank confirmed on the receipt and no mention of any other fees.

Minimum Charge $866.15
Taxable $165.22
Sales Tax $105.72
3% Tennessee Surcharge $30.94
Total $1,168.03

Unfortunately both Avis and BA Customer Services lines seem to be closed at weekends but am hoping this is not going to be the bun fight to sort out that I suspect it could be... I'm assuming I need to contact BA CS first of all.

I can see the odd thread about something similar but does seem to be a fairly rare occurrence. Has anybody had any recent experience?