If you are 55 or older at the end of your tax year (which you are) and otherwise qualify, your contribution limit to HSA is increased by $1,000. For example, if you have self-only coverage, you can contribute up to $4,350 (the contribution limit for self-only coverage ($3,350) plus the additional contribution of $1,000).

However, your contributions to an HSA must be reduced by any employer contributions made to an employee's HSA that are excludable from income. This includes amounts contributed to an employee’s account by an employer through a cafeteria plan.  Could that be what your custodian is saying...? Your employer might have contributed, and therefore you cannot increase your own contributions? Look at W-2, box 12, code W, it should show your employer's contributions. Code W amount and your own cannot exceed the above limit.