Bank refused to give us a mortgage because we had outstanding credit?

Me and my husband are applying for a mortgage and the bank refused to give us one as there was an outstanding credit in my name. It was a mobile phone account which I thought was closed 2 years ago but apparently had £21 outstanding which now are £66. We never received mail but we had moved homes and we never got an email regarding this outstanding value. If i pay it now, will my credit score improve? As it says it will show for a total of 6 years. Will I be given a mortgage if i pay the outstanding £66?

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