Ring the MCS on Monday and explain to them, you believe the company has gone bump without providing certification and ask what they can do to help. Also ask what umbrella schemes they were under – MCS registered installer code of practice schemes HIES, RECC GGF and NICEIC or Nappit electrical bodies..
Can you remember if they NICEIC or Napit approved electricians, there would have been sticker on the van or it may mention on a quote/invoice and then Speak to the original companies certifying body Certsure for NICEIC & Elecsa for Napit and see what help they can provide.