Which one? If your highest-interest debt is also one of your smallest balances, Avalanche is a no-brainer. If they're different debts, go Snowball. Motivation beats math every time if it keeps you in the game.
If they say no: "Is there a supervisor or someone in the retention department I could speak with? I'd really like to keep my business with you."
General education from a 30-year CFO, not investment, tax or legal advice.