I have two issues with my essay service provider. And I need help in identifying them and getting them to cooperate and reply.

1) I got caught for plagiarism for submitting an essay written by an essay service provider (I prefer to keep the name private as I still don't know how it's going to work out; I'm still in contact with them). Luckily, I managed to avoid punishment. My essay writer apologized and they promised to find a new writer. I have emailed them 8 times for the past 8 days, with one email per day asking them if they found a new writer. They have not replied! You would think that they'd at least respond to say they were on it.
2) Other students people who used their services tell me they've used this company and never had problems. I guess I got unfortunate. But I'm willing to try them again.
How can I get them to cooperate and write an essay I won't get caught again?
Can I find out about them and threaten them? What suggestions do you have. I'm so pissed off at this experience, I'd love to strangle them.
Do you suggest that I use a different service? My friend has suggested that he can use his email to order from them to make sure they treat my project well and I get the best writer available. But why would they not give me their best writer? Is it because I always select the cheapest option and give them a lot of time?
Thanks for advice and suggestions.