Dealer ignoring obligation to repair

[MinuteMan]

Hi,I bought an Audi TTRS in Jan for £35k from a dealer and discovered that its burning oil around 1L every 400-500 miles. I didnt take out any finance or anything. Still had my second car and wasn't driving it much so didn't realise the issue until March

I text the dealer this twice (in March and April), he has read my messages but not replied
I've sent him a letter by recorded delivery asking him to repair under CRA 2015 giving him 10 days to respond but he's ignored that too

What should my next action be, am I okay to get the issue diagnosed and repaired and then go to court for the repair cost?

I only fear that it's going to cost in the thousands

[MinuteMan]

But everything was done via text up until I flagged the issue- radio silence after then. Plus afraid that a dealer who ignores issues is also the type to:
A) Take the car to check over and "find no issue"
B) Drain the oil and fill it with a thicker one to try and mask the issue


Yes it came with 3 months RAC warranty with a £1k limit. But I went to dealer because the only local RAC approved garage doesn't have the best rep, plus the warranty doesn't cover diagnosis of the issue