Good Bike Mechanics in North London/Hornsey/Harringay?

I bought a Cube Attain GTC Pro Disc 2017 Carbon Road Bike (https://www.rutlandcycling.com/bikes/road-bikes/cube-attain-gtc-pro-disc...) last year and love it.  It's my first road bike coming from the dahon folder i used to commute on... but there's always something wrong with it.

When i cycle standing up (to go up hills or away from lights) it sounds like the spokes are being strummed, and the shifters - Shimano ST-RS505s - sometimes don't catch, and the front derailleur won't shift up from the small ring at all - the shifter just slips time and time again.

I've taken the bike to my local cube stockist for a service (Evans) and none of these problems seems to have been fixed.

Can anyone recommend a good bike shop/mechanic i can take it to in north london?  I'm near Hornsey/Crouch End/Turnpike Lane/Muswell Hill...

Thanks in advance for the help

Dave