Gas Cert not received from Gas Safe Plumber

Other

I requested that a Gas Safe plumber do a Landlord Cert for me, I posted him the key and after he had done it he left the key on the mantel piece in the house. Several months passed and I realised that I hadn't received the Cert or the bill for it. I keep asking him for it and he keeps telling me that he will put it in the post but it never arrives.

I have now got another Gas Safe plumber to do me another cert, he has found a potential problem with a fire that the previous plumber had installed only a year ago, and I have asked him to upgrade the installation.

In the mean time the tenant is threatening to take me to court for not providing a Current cert. Do I have a leg to stand on? I feel that I have acted appropriately but failed to ensure that the 1st plumber had done the job that I had asked him to do. He hasn't told me that he didn't do it, I just presume that he didn't!

The tenat is a particularly dificult individual who will try to get something out of it if she possibly can do.