Unfortunately viaBTC is the only accelerator working right now. All others seem to be fake.
viaBTC allows 100 transactions per hour to be accelerated. You need to submit your TX within the first second(s) of an hour.
Are you in control of the recieving address? If so, you can try a Child-pays-for-Parent.
If you are not, either the reciever can try a CPFP or you can try to double-spend your transaction.
When double-spending you have to follow these basic steps:
- Let your wallet forget about your TX
- Create another transaction with a higher fee using the same input
- Try to broadcast the TX
If broadcasting the transaction fails because of a mempool conflict you can still try to push the TX via online services [1].
Depending on the wallet you have used the steps above may be more or less easier to accomplish.
[1] e.g. https://blockexplorer.com/tx/send, https://www.smartbit.com.au/txs/pushtx, https://live.blockcypher.com/btc/pushtx/ or https://blockchain.info/pushtx