I tried redeeming it on coinbin and signing it, but got error 400 when i broadcasted.
Did it show any kind of error message? It may just be a broadcasting or connectivity to remote server error, in which case you can use an explorer like blockcypher to try and rebroadcast the same transaction if the signing was successful and the issue was only when broadcasting it.
Can i send the redeem script and public key here so it can be easier for you to help? That wouldn't give away access to them, right?
There is no need to post it here if it looks like the following (the bold part should be the same and the rest should be of the same size which is 40 characters equal to HASH160 of your pubkey):
001479091972186c449eb1ded22b78e40d009bdf0089