Implication of withdrawing after signed contract due to First advantage.

I got a role on the finance team about a month ago now. I have signed the contract and completed all the necessary paperwork.

However, the company Citi use for these background checks ( first advantage) have been nothing short of an absolute f*****g nightmare. They come back to me every other day with the tiniest problem and I still dont believe theyve even bothered to start the background check.

In the time this has taken ive received another offer from another firm that in going to accept. Are there any implications of me withdrawing after signing the contract? Ideally id like to .ake Citi aware how horrendous of a process first advantage have made this