UK Landlord Forum / Life

I was introduced to a company that takes private lettings and sub lets them to vulnerable people whilst monitoring them daily/ weekly and offering support and counselling whilst maintaining the property. I went with them because the fellow landlord who introduced me had a good history of working with them, the idea of doing something decent appealed to me and the local council funded the (higher than average) rent.
The insurance and gas safety are still my responsibility and I'm really struggling to get the company to tell me whether or not they have completed the gas safety check. I have it in writing that they booked it for the 6th of October but they won't tell me who inspected the property or provide me with an invoice for payment or copy of the certificate. Needless to say I don't think the jobs been done. Several emailed enquiries have been answered with a general "we'll look into it" response but nothing more.
Obviously I'm concerned for the tenants welfare and equally my legal position.
The nuclear option is to threaten reporting them to the council/ HSE but how liable am I and is there a less drastic option? The tenant is theirs and I don't have their details as they are a vulnerable adult so I can't just go barging in especially in lockdown 2.