I have a second box that I have turned on for the first time and got the error code 7400 bouncing around the screen on every channel (not every channel is available for some reason). Having read other threads on this I got in touch with technical services who tried sending some signals or something and getting me to turn it off and on again before they said there was nothing they could do but to try phoning them again in a few hours.
Error 7400, as you've realised, is an activation error which can only be resolved by calling C/S (either 150 or the dedicated 9539500 number)
If C/S have told you to wait a few hours, I'd suggest querying with them why that is. Perhaps there's a delay sending the reactivation hit, perhaps there's a problem with it, maybe it's indicative of a problem with your box.
Either way, I'd suggest calling back and trying to establish what the delay is caused by.
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