When my parents leave on vacation and I'm house sitting, the house receives almost no spam calls. When they're home, they receive at least two spam call a day. What could cause that?
If they leave for a month, spam calls stop almost immediately, within a day or two of their departure. Happens every time they go on vacation, twice a year for 3 years now.
Their landline is super old, in the phonebook still, and in a ton of leaks related to my fathers old accounts, so spam calls aren't unexpected, but it's unusual that they stop almost entirely when they leave the country. The calls also aren't even good scam calls, like you'd expect if they were sophisticated enough to know someone wasn't home. Standard local number but caller ID is the number repeated or "UNKNOWN NAME".
Compromised accounts doesn't seem like a possibility, I'm in charge of all their passwords which are high quality and their laptop, which they use for work only. Their phones are fine, both Apple devices with no jailbreaks going on. Router is up to date but we do have a static IP that hasn't changed in like 20 years.
My one theory is that someone is tapped into the telecom system somewhere (not locally, but like a company level breach) and truly does see that no calls are being made or accepted. I don't use the landline, I don't answer any calls, no voicemail. But that just makes no sense, their entire MO is to just war dial so much that sometimes no scammers are even available if we do answer.