It is not a problem everywhere. I do not get snail mail spam or call spam in Germany. For post it was enough to put up a sticker that forbids advertisements. No idea really why call/sms spam isn't a problem.
I envy you. You're either incredibly lucky, or Germans are really law-abiding.
Here in Poland, the sticker that forbids advertisements does jack all. The post office might stop delivering spam, but most of the garbage in my mailbox comes from private individuals, hired by local companies, delivering the spam personally.
Call/SMS spam dropped somewhat thanks to GDPR, though I've experienced a uptick in the past few years, primarily driven by cryptocurrency scammers and fly-by-night companies selling photovoltaics. I do get an extra amount of phone spam, because I had a business and my phone number is listed in the business database.
Note that I do consider first-party (as in, from companies I have relationship with) cold calls as spam and scam too. Telcos in particular are notorious for scamming people - at this point, there is not much of a difference between scams discussed in this thread, and technically legal upsells and bullshitting done by my phone operator.
(They're not that better off-line, either. Only few weeks ago, a sales rep from a high-profile salon tried to scam my grandmother, by deceiving, manipulating, outright lying and using psychological pressure tactics, to get her to sign for a TV and Internet service she doesn't want or need. That happened physically, in the salon, when she went there to take over my late grandfader's phone contract.)
