Beware of binary "credit" in your account. Often, that's a bonus with many strings attached.
Tell them you'll be thrilled to sign a document promising to ask that this issue be marked as resolved and to take no further action against them on the basis that they credit your account and process a withdrawal for 100% of your money (including that promised credit).
So, then the order of events would be:
They present you with a fair document to sign (including pre-defined time limits, as shown below).
You sign and send them the document by a mutually agreeable method.
They then have a pre-defined time limit to credit your account, return all funds due to you, and close your account.
You then have a pre-defined time limit to come back here, state that you got everything you were looking for back in your bank account, and ask that the issue be considered closed. Further, you are barred from making any new claims relevant to this issue or anything else related to the closed account.