Did you use the coinomi and exchange your coin to other coin using changelly?
Honestly i am always using changelly but i haven't any issue yet my guess maybe you pay less fee that is why your transaction still not received to your other coin wallet..
Can you share the address where your coins from and the receiving address where you should receive the coin?.
So that we can check if either your transaction confirm or not..
I also used Changelly in Coinomi. Even with usual fees I had to wait up to 24 hours (BCH Doge) on cryptocurrencies with quick and stable network. But you are right to point out, that users shouldn't change fees. (They can be changed on settings as default fees)
I would anyway don't use changelly anymore. They have many complaints.
There is another aspect to care of: Changelly supports many coins. On some of them wallets must be upgraded very often, so that transactions could take several days.