Can a collection agency acess your safe deposit box?

No, only the bank may access your safe deposit box, and then only after you allow the lease on the box to expire. Once the payment for the box expires, the bank must wait a certain amount of time (this is laid out in the deposit contract and in some state laws) and attempt to contact you to either collect your belongings from the box or renew your contract. After this period elapses, you are considered to have abandoned the box to the bank and the contents become the bank's property. However, if you leave items such as a deed or a title, you still legally own that property - the bank has a piece of paper that says you own that property.