Shimano deraileur issues

[miss_emma_jade]

Im really struggling with the first new bike ive purchased in a long time. It wasnt hugely expensive (mongoose crossway) but its a good comfortable ride and i have upgraded a few things already. Ive been getting it serviced as it tends to do about 70km a week, and so far its probably done about 500 km i guess. This morning on a busy road the chain came off the front cassette, and really screwed me up, as i changed from mid to high. Lately it hasnt been changing down imediately either, so generally its a pain. So its been serviced a week ago by the lbs where i bought it, and in that time its got bad again. So... what do i do? Keep taking it back? Learn to adjust them myself? Upgrade the gear system? Buy a better bike? Is this normal? Help someone!

[Red Rider]

If it's still within warranty then the lbs needs to have it fit for purpose. If they want a happy, long term customer, the same applies.
If it keeps happening after servicing, they should replace the suspect component/s.

[Calvin27]

Buy a narrow wide chain ring for $50 and be done away with the primitive front derailleur system for good.

[systema83]

Altus is usually serviceable once properly adjusted. If your LBS has just serviced it, I would suggest you to take it back for adjustment as they obviously didn't do it properly. You probably also want to look for another mechanic if you prefer not to DIY in the future.