what battery do i need? 40mh or 70mh

i purchased a battery from eurocarparts

Amp Hours (Ah): 40AhCold Cracking Amp (CCA): 330CCALength: 207mmWidth: 175mmHeight: 190mm


lion brand, however when i took it for servicing they said it was the incorrect battery even if the car reg indicated the battery on the ecp website...
they said i need at least 70ah? and thats the reason why sometimes you car doesn't start (a problem i have been having)

can anyone suggest me a battery to buy for the car? its a 2011 vw mk6 1.4

thank you

The battery i bough for my car(Granted was a GTI) was Cold Cranking Amps:730 ampsCranking Amps:910 amps