How to avoid shipping / delivery problems?

I have a small online business and I ship products all over the world. Now, my business is growing and I am.
More shipping / delivery problems that affect my business.

Some examples:

– The orders disappear (plot tracked). Tracking number states the package has been delivered. A search would take several weeks. Do I have to replace the order immediately every time I run on my own?

– The customer gave me the correct address, but the package could not be delivered due to address problems. The items are returned to me, but do I need to absorb the shipping costs? This happened twice with the same address.

Excuse me, maybe there are really direct answers to this, but I'm fairly new to running my business.
As soon as I try to get information from the delivery companies, I end up in a loop or the answers are vague, as they do not want to treat the packages as soon as they leave the country.

Is there a term and condition regarding the small business shipment that I can recommend?

Thank you very much for your help!