The websites which @Struppi mentioned do work but you have to find website that has overall very low traffic considering that many people try this method. Just keep checking all the numbers present on the site and you may get lucky and manage to activate your account.
Since the apps @Struppi mentioned do not work in my country, so I was unable to try them but I have heared from different sources that these apps indeed work so you should give them a go too. (Side Note: Most of the "legit" numbers in such apps require you "real" phone number for activation or you have to pay for them. Some of them are free too but are not guaranteed to work.)