Secured loan on title deeds from 1991

Lemonade99

Hi ,
I hoping for some advice.
We are trying to sell our late parents house and it has came to light that there were 2 secured loans still on title deeds.
One from Bank of Scotland for their mortgage (paid off in 2004) and one from Avco trust (paid off in 1994).

The BOS has now been removed but Avco trust ceased trading in 1996. They were purchased by Citibank but they have no record of the account for Avco trust.

Our solicitor is now contacting the people who own Citibank but has been waiting over 6 weeks on a response.

We have no documentation to prove the Avco one was paid off but I remember my Dad paying it when he retired.

My question is , what happens of Citibank group cannot find the record ?

Can we never sell the house ?

Thanks

Lemonade99

Appreciate this is most likely in the wrong forum. Apologies. Can't find a way to delete it.