Help!

We have recently moved and 1 of the showers is partial to a bit of mould and it is driving me nuts!!!

It seems to be mould spots in the grout and I have tried using mould remover and Enjo calcium remover (which is great normally) but some of them just aren't budging.

What does everyone else use? Any tips for preventing it in the future? It makes me feel like we have a dirty house, which we don't have.