Why is it so difficult to email or text them with (as I do) "sorry I can not meet you again" ? It is not rude but is clear in what you mean. Then you can choose to block or ignore if they persist in trying.
I think quite a few providers are frightened and rightly so because some punters/clients do not take a 'no thank you' very pleasantly.
However I think it's only fair and also stops most from continuing to try make contact........it's only a few who will turn nasty. A few more will ask for an explanation, some will ask for a second chance - polite no thank you usually means they can move on.
The ones who get nasty need a reminder that harassment is an offence that the police would be happy to discuss with them, however not every sex workers is either in a situation where they can, or wish to deal with the police.
So it's not as easy as it seems, however as I say being clear just stops the keep trying behaviour. Also stops the guessing games for those who just can't reply, I've had a few regulars wonder if my busy non-response has been because I'm trying to tell them I don't want to see them. I now always make it clear with new clients that if I ever don't want to see them I will tell them explicitly.