Giffgaff do not have a fair-usage-policy on their "unlimited data", as many of you will know, and have been known to boast that with giffgaff unlimited really means unlimited.
Having recently learned that it doesn't, my suggestion is that giffgaff stops claiming that it does, and put a number to the data usage limit.
I'll provide more details in the comments.
Where did you learn there is a FUP?
This has been suggested a few times recently and duplicate to this idea
In recent weeks I have had cause to use a higher-than-average amount of data, but since I was on the £10 goodybag, I figured this would not be a problem.
How wrong I was.
Without warning, I received an email from giffgaff informing me that they thought I was tethering, and that as a consequence my mobile internet would be cut off shortly; and it was.
In response to this I sent a message to an agent explaining that I had not been tethering, and asking for my internet access back. After a few weeks of to-ing and fro-ing on the details, I was told that I had broken the terms and conditions anyway, because I had used a sufficiently large amount of data that it would be having a negative effect on other users. Following this, I apologised, and said that it would not happen again; that I had thought I had unlimited data, but I would try to keep my usage low from now on. I was then told that my case was being raised to head office, and that following their approval I would get my internet access back. The next message I received was informing me that head office had refused my appeal, and I would not be getting my internet back.
So in short, without warning, I had my internet taken from me, never to be returned, all because I crossed some invisible line at which it begins to affect other users.
Why bother killing a selling point of giffgaff? This idea basically is saying to make the network worse, and this network was designed to be best for value.