that is possible what happened to OP, unconsciously copied and pasted a BTC address
@OP can you check whether 3L8yH... is one of your BTC receiving addresses on coinbase?
or might as well contact coinbase support and ask whether BTC address 3L8yH... belongs to them
and explain to them you may have mistakenly sent BCH to your coinbase's BTC deposit address
I think when you make a mistake when sending funds in the form of cryptocurrency or bitcoin to the wrong address then it will not be possible to make a refund, because I have experienced it like that and have contacted support but did not give good results. for the OP there is nothing wrong with trying. hopefully the assets can come back.
this is not in the sense of asking for a refund, but asking for a help to rectify a mistake
if that BTC address 3L8yH... actually belongs to coinbase, then they can also access BCH address pr994haj...
it's a matter of coinbase's willingness to help recover those coins and credit the user
(cmiiw) their policy is if the value of that deposit is over certain amount they will recover it for a fee