@robert1997 that would depend upon what you are changing. In theory doing it online should mean you see precisely what you are ordering (and can take screenshots if you wish) . However sometimes the online process does not appear to give me precisely what I want so need to phone, Doing over the phone .. you don't see what the remote operative is actually doing. I normally only proceed with a phone order if I am convinced the operative knows what they are doing and I always clarify dates and any impact on or new minimum period contact terms.
Thanks @zulu17. I prefer online but am always afraid of losing current offers I have taken up. Never thought of taking screenshots so big thank you for that piece of advice. Like you I do be concerned that the person I'm talking to over the phone is doing exactly as I expect them to (and this applies to any service I'm dealing with) so I also tend to check , double check , even triple check everything is as I want it to be. I'm sure they think I'm cuckoo but sometimes its the only way to get peace of mind all will proceed as planned. Many thanks @zulu17.