How can someone use my email to purchase service or products?

So I get random receipts of services being paid or needing to be activated and eventually almost immediately that service becomes active without any submission from me. This includes product purchases. I do understand emails can be mistakenly entered and some receipts are obviously that. But I get my email used in places like Africa/Philippines etc where I never do business.

So I ask this seemingly weird question of how can someone pay for services and products using my email address without actually using my email (i.e. clicking on links to activate etc)? It's gmail and I check to see where it's used with "Last activity" link that shows IP's and device endpoints. Nothing shows my email is being accessed outside of my home. I change passwd and use 2FA.

Can someone shine some light on what's been baffling me for quite sometime.

PS> Also check my credit and shows no new loans/CC etc...

PPS> Jesus.. is it possible that a trojan living on my PC stole my session info and is able to use my opened browser and hijack emails??@!