Intec college outstanding balance and NOT responding or communicating in 5 years

I studied with Intec College and had a debit order.

Now that I ma in the process of buying my first home, there is an amount of 841 outstanding on my account.

They have not contacted me in 5 years about this outstanding. When I phone they put me through to collections that cannot help me with my query. They keep putting me on hold and putting me through to other people that cannot help me. HOW am I going to get this removed from my name?? I am 100% SURE all my debit orders went off!