It's a perennial niggle this one. Some agents will not charge if you can't do it on-line; some take the view that changes are chargeable only if you could normally make those changes on-line but for some reason (i.e.: website issues) you can't.

The normal advice is to call up again and repeat until you find the pragmatic / sensible agent, or get bored of asking.

Don't get too excited by this possibility, however. I've had an agent who saw that I had been under-quoted a price in miles to upgrade with an offer to waive the fee because it couldn't be done on-line, but then refused to honour it! So, the lesson is if you find a nice agent, jump immediately!