I'm a legacy user on T-Mobile, not EE. This a log of my experience for readers' information, and not a complaint or request.
On 29/7/2017 I bought a 6-month-web pack, it expired 28/1
On 11/1 I bought a 5-day pack of unlimited data (and other things), it expired at 23:59 on 16/1
On 16/1 at 17:09 I received a message saying I had used up my Internet Booster and it would reset on 23/1. This was while my 5-day pack was still running.
On 23/1 at 15:20 I bought a 1-month smart-pack giving me 1GB of data
On 27/1 at 17:48 I bought a one-day pack of unlimited data (and other things). It ended at 23:59 on 28/1
On 27/1 at 17:58 I received a message saying I had used 80% of my fair usage
On 27/1 at 18:45, according to 'AL->150' I had no data
That's all quite involved and I don't expect anyone to read and take it all in, but I have a few points
I never got the 5-day pack to work, according to the display on the phone data was being sent but nothing received. I phoned 150 and was put through to technical support and they tried really hard, eventually suggesting that I update the software on my phone.
On the other hand, the 1-day pack worked really well. I was very pleased with it.
It seems to me though, that the data from the 30-day pack was used even while the 1-day pack was in use. When the 1-day pack came to an end I had no data left from that 1GB but the record on my phone suggest that I should have. I may be wrong.
I strongly suggest that anyone who is contemplating buying a 1-day pack use 150 to check their data allowance before and afterwards.
I've had excellent and generous service from EE and I'm sad to be leaving them but I'm a low volume user and '3' have an offer that comes in at half the price.