Incogni & Alternate Phone Number

Two suggestions in one:

First: use an alternate phone number that is NOT your cell phone specifically for things like signing up for discounts/purchases. Use your real cell phone number for banking, doctors, stuff that you actually want to hear from immediately. Use your alternate phone number for everything else. This makes it so your alternative phone number is the one getting passed around the internet and that translates to fewer spam calls. Right now I use Google Voice, but I'm looking for non-Google alternatives.

Second: get Incogni. It's a service that will trawl through the internet looking for your personal info (phone, address, etc) and automatically send requests to get your data deleted. It's VERY effective and since I've started using it spam calls and texts have decreased by a huge number.

Third, iOS only: Effectiveness on this will vary, on iPhones you can screen unknown callers either by just sending them straight to voicemail or asking them for the reason for their call before telling you if it's a real call or not. (https://support.apple.com/en-us/111106)

Fourth, just in case: Make sure you are on the national Do Not Call registry. Won't fix everything, but every little bit helps.