I had a similar problem, got vodafone to rectify it. wifi worked fine, ISP APN that I was on was causing problems. A different APN setting with the same provider had no issues, but my Mobile package billing was with the original APN. second one would cost me alot.

The mobile operator must have change your settings, they probably change you dns or add filters on your traffic. You have to contact them.
Did it ever get redirected to another page intermittently. If it did recorded it and tell them. It will give a good technician to find the cause of your problems.