repair job not up to required standard

For the past 6 months I have been taking in my car for the same mechanical problem of which I've been repeatedly told it's a sporadic fault and every time I get it back, the service reps would claim and conclude the problem is fixed, only to turn out the problem would persist. On Monday the 4th I took the car in for the same persistent problem, it was allegedly fixed only for the same problem to start again today on the 9th of Jan 2016. Now at this present moment I'm really gatvol and I feel if Audi the Glen is not willing to fix this problem, then they should rather take back this flipping car of theirs and give me a new one, but I will not continue going back and forth to the dealership for them to keep not fixing the problem. I pay instalments for this car which is on maintenance plan and this nonsense is unacceptable. If they think they Will only address the real problem with this car once my maintenance plan has lapse, then they must know they Will have the ombudsman to deal with because I have kept every record since the car has been going in for this problem. I want this car fixed to perfection as in yesterday, I'm tired of this nonsense.