Cucumbers sown from seed get to approximately 3″ then start to rot from the top. Tried too much water, too little water – moving to a different area, cold frame – greenhouse – indoors – nothing seems to work.
Cucumbers wilting from the top sounds like a cucumber wilt disease. This article has more information: https://www.gardeningknowhow.com/edible/vegetables/cucumber/bacterial-wilt-cucumbers.htm
The best way to get a positive identification of problems is to go to the county extension service (in the US,) or the master gardeners assoc (in UK.) You can also seek assistance from any botanical garden or university horticulture program.