Numerous questions - issues with mobile network connections

[pmfrench]

Hi All,

I have a few questions which I hope some kind soul can help with.

Firstly, background - using Huawei Y300, running android 4.1.1, on Tesco mobile (uk)

Been running mobile network perfectly fine for 2 weeks but all of a sudden having problems without any reason I can think of. When running Chrome or the stock browser app I'm getting error messages like Error 101 net:: ERR_CONNECTION_RESET which seems to be associoated with proxy settings. The mobile signal icon is on and it has a H present which suggests to me it's getting data.

What I'll also say is I'm not sure whether the handset is SIM locked, but i was told that it wasn't by the store assistants (Carphone Warehouse).

1) Does anyone know what might be causing this error?
2) Do proxy settings apply to mobile data (I don't know)?
3) If a phone is locked would it mean you generally can't do anything, i.e. could you have a situation where you can make calls etc but not use mobile data.
4) Is there an easy way of determining whether the handset is locked?

Thanks in advance all, and if there is any further info needed let me know.