Hi Ernestas, and thank you for getting back to me
The Huawei router is a B311s-220, looking at the network profile in the B311, it shows the APN as '3internet'. User name & password are blank.
The TRB140 has been working at full speed with '3' for months, something 'happened' from last weekend and now shockingly slow - without any changes being made.
P.S. I did a factory reset to the TRB140, but no joy. I states it's running on the latest firmware