My wife had a loan secured on the house which was before we were married, my wife was killed in a car crash and it took this company over 3 months to contact me. They have added lots of interest and also a early repayment fee. Is this legal can they add interest to this account

Sure, if that's what's in their contract.

Loan contracts are simaler all over but not always identical. The interest they may be able to charge but they might not be able to charge the early pay off fees because of the situation. It would be best to consult a realestate lawyer near you for that answer as it does vary.

OK, your wife, so you knew of the loan on the house ?

You contacted them and informed them she was dead and who was going to be over the estate?