(Assuming that it was a public highway, rather than a private road), double yellow lines no longer require any form of roadside signs. (The law was changed, to that effect, in January 2003. The only exception is where the parking restriction is 'seasonal', such as at seaside resorts). Double yellow lines indicate that parking is prohibited 24 hours per day, 7 days per week, so no additional signing is required.
However, double yellow lines on the road do not prohibit 'loading'. If there were no yellow lines (either single or double) on the edge of the kerb you were entitled to stop to load bulky goods, as long as:
(a) you weren't causing an obstruction ;
(b) you'd paid for the goods prior to stopping your vehicle at the roadside ; and
(c) you were there for the minimum amount of time required to load the goods (and for no other purpose).
If there were double yellows lines on the edge of the kerb you were not permitted to load at any time. If there were single yellow lines on the edge of the kerb, loading was prohibited during the times indicated on the roadside plate. (The presence of such lines is sufficient to tell you that you must look for, and read, that plate if you intend to stop for loading).
If you were genuinely loading, within the conditions specified above, and there were no loading restrictions in place, you've got good grounds for an appeal. (However it's worth noting that traffic wardens and council parking attendants are usually instructed to wait several minutes, before issuing a ticket, to see if anyone has actually stopped for loading). Otherwise you should just pay up.
Chris