I believe that all Orange do is basically give you a <contract length> subscription to Deezer Premium with the added benefit of mobile access (this is a Premium+ feature which usually costs £10 a month) so I'd probably contact them with this issue if you want a fuller explanation.
Yes. I have no idea why this isn't made more obvious (apparently one of the top asked questions at the moment) but it is. Basically all data going to Deezer incurs no charge. I expect it's probably an internal traffic route via vpn to deezer itself in france or via cache server in the UK but either way, you don't pay to use the service in any way, shape or form.Is the 3g data really free on this app?