Repaying doesn't release your collateral on its own. You need to repay everything, then close your Credit Line.
Open your Credit Line and tap Repay.
Repay the Full Payoff Amount, which includes today's interest.
Tap Close Credit Line and confirm.
Your collateral then returns to your Wallet.
If You See Balance Remaining
You still owe a small amount, usually interest added since your last payment. Repay it, then close your Credit Line again.
If You Only Need Part of It Back
You can withdraw some collateral without closing your Credit Line. See How do I add or remove collateral?
Still stuck? Contact support.