There were recently the same topic in forums, I have saved the links that were posted from this topic, maybe it can help you further:
https://bitaccelerate.com/
https://btcnitro.com/

I use them both, but nothing heapend. My tx is still unconfirmed. After 30+ hours. Sad

I have not tried to avail paid service. Submission here is always beyond the limit.

I'm just using the free service.
Just as I've said, you need to check the time correctly and accelerate at exact xx:00.

Whenever I try this service always got "busy" notification.