The problem is when you planted it, as in the time of year, most likely. I hesitate to say this because for all I know you've been drowning in rain since you planted the clematis, but they need lots of water applied directly to the base of the plant and frequently, until they're able to put out their own water seeking roots. You also don't say whether it's in the ground or a pot, but I'm assuming in the ground, and how close did you plant it to the fence or wall behind? If it was less than a foot away, it may well be in what's called the 'rain shadow' meaning the rain does not get on that area of soil very much. Water weekly with about 5 litres, move further away from the wall at the end of the month if you've planted too close. Do not feed at this time of year - clematis in the ground only need a handful of Vitax Q4 or fish blood and bone or something similar raked or lightly forked into the soil around the base in about April. Feeding of anything other than annuals should be stopped by mid July at the latest, as a general rule.

There's also the possibility that too much bone meal was in contact with the plant - I've know this apparently kill things, unless I was just unlucky.