Hi Pete,

Have you tried all the keys that came with the padlock? If the padlock is outside, Sometimes at this time of year small insects and even woodlice climb inside to keep warm, please try to use some wd40 or similar in the lock, Give it a few moments and shake the padlock before trying the key again. 

Hope this helps. 

If not please email me at Contact@dktools.com and I will assist you further.