Even if you haven't expressly reserved the right to terminate, the deposit contract is open-ended as to expiration, and you can terminate it without having to provide a reason. Just be sure to determine first whether you have provided for a notice period in your agreement, and give notice accordingly.
And avoid including the ubiquitous tagline in your notice: "If you have any questions, please don't hesitate to contact us." You don't want to invite questions, and you aren't trying to be customer relations oriented here. You are telling the customer the account is being closed.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8