My tl-mr6400 will not connect to the internet with an o2 sim card but it will with a Vodafone sim card. I know the o2 sim card is ok as it works in another device.

I want to use the o2 as a new mast has recently been installed nearby and reception will be better once I get it working. I have seen other posts similar to this but the replies seem to assume we are all experts. I am not a technophobe and can follow simple instructions so please make any solutions as simple as possible.