The Big Bad ISP?

I have told this story so many times, I forced myself to tell it once more, so I will not have to again :D

For months now, during certain times of the day (early evening until 11PM), I have been unable to use the internet, with the exception of HTTP, which is web browsing. All other attempted connections fail, transmit a FIXED amount of data (I think it is 1Kb, but I have not yet counted) and then hang, or the data packets can simply arrive delayed... often by hours.

I can't state for definite that this is my ISP filtering traffic. How can I? They have not announced they are/will, though they do 'reserve the right to at any time'. Until I get a definite answer from them, I shall not write their name here.

I am hoping to resolve this, (currently battling with their seemingly non-English technical support), on the basis that this problem severely limits my use of the internet. I shall switch my ISP if all fails.

To be continued...