If the battery will turn the engine over but is still doesn't start then you have a fuel or ignition fault
First check the battery, if battery is not in charging condition then check the alternator and the self starter
You have possible alternator fault but may have a parasitic power drain. Do check all connections for corrosion etc. .
If all four battery connections are clean dry and tight do the following:
#1. Touch the battery terminals with an inexpensive volt meter set @ 20 volts with the engine running. IF the alternator is charging peoperly the volt meter chould read between 13.5 - 14.2 volts.
#2. A trusted private mechanic will do a starter amperage draw test.
#3. There is an outside chance your car has a parasitic amperage draw when the engine is not running. The dealer of the car is best equipped to find the problem.
take it to another garage, blimey if the garage cannot see what is wrong, then what chance of us/ what is taking the race out anyway, am I being thick?
So I need some advice I have a seat Ibiza 07 plate and it keeps failing to start I had race out and replaced battery it worked for a while then started failing again so had battery swapped it work for a few weeks then failed to start jump started off another car and then was fine for a week then needed to jump it again, it is failing to start more often and sometimes when I jump it still won't start but if leave it a day then jump it will start, took to garage and he is unsure if altinator or starter help