Have you checked your phone settings to see if by any chance the settings have gone from GSM/WCDMA to GSM only? What phone are you using?
They are different communications channels/subsystems.
And the channel rather than the CPU/SoC data processing will always be the bottleneck.
As such I disagree that the wifi speed is in any way relevant to the query here about carrier data throughput/rates.
But I'll leave it at that as the theoretical discussion is not really answering the question posed.
What does your online account say about your membership status, expiry date and allowance balances?
Hope this helps.