Clients asking for their deposit back

I recently began working with a client on their website. After a bit of back and forth and us trying to fulfill their ever-changing brief they decided that we were not the right fit after all. We received 50% deposit upfront. The client has not, in over a month, contacted us about negotiating how much of their deposit they want back. Our T&C's at the time did not state that the deposit was non-refundable but I would not be happy to pay it back as we did everything possible to do what was required from us. I am worried that if I start to utilise the deposit money they will come back in a few months time and ask for it back in which time it might not be there. Is there a period of time where it's open for them to ask about it, after which it's no longer available for them to ask after?