carrot tops disappearing

hi , im a fairly  new grower this year ive put 6 1.2x1.2 mtr beds in and a 2x4 mtr polytunnel with a large raised bed ive no problems with the beds outside but in the poly tunnel every night or two one carrot top disappears it looks like its been cut very close to soil level  ,   this is only one at a time and from different part of the raised bed  ,   ive tried turmeric around the tops but one went last night   ,   dont think its slugs/snails as it looks like there cut of or chewed there is no carrot top left no debris nothing   ,   if anyone has any idea i would really appreciate some help  ,   in the raised bed from right to left i have cucumber , dwarf peas , carrots , onions , turnips , more carrots , radish , lettuce , spring onions , more carrots  , in that order ( it a big raised bed 3 x 1 mtr made from scaffold boards)  the  carrots affected were bought and the ones i planted from seed are not  ,  carrots are only up to  2" high and the ones unaffected have only the two first leaves , the others have the new fluffy tops , i thought maybe a mouse or some sort of beetle , many thanks in advance