TransUnion-Phobic

I’m in the market for my second btl. I recently tried to transfer a credit card balance to one with nothing on it, only to find no one would touch me. I downloaded CreditKarma and found a missed payment to Scottish Power.
After a phone call it turns out they’ve been texting me for three years to settle a £16 bill from when I first let my BTL. I thought the texts were from scammers as an email from Scottish Power three years ago said my final payment would be taken by direct debit. Scottish Power made no other attempt to contact me only texts.
Is this going to affect a mortgage application?