It is difficult to tell from the limited information you give. If the business was a limited company, and if you had given a personal guarantee to the bank, and if there was no overdraft when you sold, and if when you sold you told the bank that you were terminating your guarantee, then the answer is that you are not liable for the debt. The key is that there had to be no overdraft, and you had to tell the bank that you were terminating your guarantee. That would fix you with a lilability to honour the guarantee to the amount then owing which would be nil.
Did you not have professional advice when you sold? if so your advisors should have sorted this out for you at the time.