Although I haven't sorted out my mess yet, I think it is safe to order over the phone. The problem seems to be internet orders as they are dealt with by a different department - you can't speak to them, emails take at least 24hrs to be answered so it is impossible to have a conversation and the customer helpline don't have any records of internet sales on their systems.
If you ring up they will confirm the order has gone through and you can call back and check the order at any time. The problem with using the 25% code is that you need to open an account which involves a credit check. I have been informed that often your initial credit will be limited to £100-£150 until you have placed an order and paid successfully. This will obviously mean that you cannot buy a £600 TV and your order will be rejected after 5-7 days.
The only way I can see to be sure is call up, use the 20% code (place the TV in your shopping basket, go to checkout and it will appear automatically in the box) and pay by credit card. No credit check, no chance of your order being declined and you have still saved £120. If they refurse the code, refer them to their FAQ section where it clearly states
"How do I claim my 20% discount off my first order with you?
Welcome to Freemans. To help kick-start your shopping, we’d like to offer you 20% off your first order with us. Make a note of the Offer code before you start shopping, and remember to enter in the box provided on the shopping bag page. This offer is only valid for new customers spending £40 or more in a single transaction with Freemans"
No mention anywhere of having to open an account.