Problem with Nissan Micra auto - gears? - Car experts help please!?

I very much doubt that they caused any damage, it's most likely just a coincidence. The Micra’s automatic transmission is the CVT type (belt driven) opposed to the standard automatic 3 : 4 gear-box. They did have terrible trouble with them to start with but seem to have overcome that. I'd suggest you take it to an expert, it might be something easily fixed.