If your contract is up or coming to a close, then Retention Dept is the only way to go, problem is to talk to them you have to convince them your off else where.
Both my deals are currently set through Retention, EE, 2000 Mins, Unlimited Text and Unlimited Data £14 (T Mobile Plan) and my main Number, Vodafone, Unlimited Mins and Text with 4gb Data, £8.00.
Wish I hadn't posted this up now,

just had a call from EE telling me I would need to upgrade to an EE plan, as Im currently on an old T Mobile Plan and there not playing that game anymore. She went through the motions and tried to palm me off with a simple EE plan worth 14 quid with hardly any Data on it, dont think She realized I had Unlimited Data.

Having looked into the Data side, she come back and offered me 50gb for a discounted £49.99pm .

, not something thats on the there Price List, but something she pulled out of a Hat so to speak, not happy I asked to speak to someone in Retention.
Having spoke to the Guy in Retention, He offered me 50gb EE Data deal for 29.60, when asked why I couldn't keep the unlimited Data plan, he replied, you can, its just that we cant give you the discount on T Mobile plans anymore (apparently, Ive been on a -£8 discount for the last 4 years) so the plan will go up from 14 to 21.99 if I stay on the Unlimited Plan.
So, Mr B, just to remind you once you come off your T Mobile Plan you wont be able to go back on it, so should I put you on the new EE 50gb for 29.60pm, He asked?, Sorry, I replied, just remind me again why I would want to pay 29.60 for 50gb, when I can stay on an Unlimited Plan for 21.99??. so He kinda laughed, and said thats fine, you wont need to do anything, just stay as you are then.