Spam texts from email accounts on iPhone

How do I stop spam text messages from email accounts on my iPhone 5s running iOS 12.4.2?

The scam spam emails to text stopped for a couple of months, but they have started back up again recently. Most appear to hawk some sort of quick cash loan. I used to get anywhere from 3-6 of these a day, but I knew the first time I got one that it was a scam, or a way for some hacker-thief to get into my phone, maybe even take it over, by downloading malware, but only if I was an idiot and clicked on the link in it. I've never fallen for any of their tricks though.

I first started getting spam texts from email accounts in early 2019. I couldn't find anything about how to stop them, or block them, so have just been deleting them. Whoever is sending them never uses the same email account twice.

I called Apple Support about it, but they had no answers. Then I looked here and found one answer, but it didn't work for me. So, I've yet to find a solution.

I have tried going to Add Blocked Contact at the bottom of the Blocked numbers list, but my phone would not allow me to add it. Maybe I didn't do it right?

Scrolling to the bottom of the list to add a blocked contact took a while too. I have so, so, soooo many phone numbers blocked.

Any help would be appreciated.