For most travellers something goes wrong when traveling for several months. It could be missing a bus or catching the train to the wrong city just because of wrong directions or silly signs you couldn’t understand. That’s just life and part of traveling! And hey, this may be where you’ll get the best adventures on your trip because you will end up in a situation or a strange place that you never thought of.
For the more serious problems you need to react in order to get things fixed. If something goes wrong, e.g. with your flight bookings, adventure tour, hostel/hostel booking or car rental, then you must react immediately to claim the missing product or service. Please contact the most obvious person in relation to your problem. This could be your travel agent, the tour operator or car rental company etc.
In any case, if you leave the matter for too long or until you get home, you may not be eligible for reimbursement or other compensation. Always try to document as much as possible and make clear written reports with facts which will make handling easier and faster. Most problems can be solved while traveling, while other cases such as disputes have to be settled upon returning to your home.