Advice please for a lurker - not a poster 
Earlier this afternoon I travelled from Manchester Airport to Chester. At the airport station I asked for two singles using our two together railcard. I asked for “the cheapest ticket” - and specifically mentioned “I want a split ticket”. The clerk said it would cost £26.80 and that no split ticket arrangements would be cheaper.
With the 14.11 northern service to Crewe to depart in three minutes I was in no position to argue and reluctantly paid for two non split singles.
On the train I found out that splitting tickets at Wilmslow would appear to cost cost 17.80 plus 4.20. I appear to have been overcharged.
Thanks everybody in advance
Two questions arise:
1 Am I right on the fare calculations?
2 How do I complain about being mis sold my tickets?

Earlier this afternoon I travelled from Manchester Airport to Chester. At the airport station I asked for two singles using our two together railcard. I asked for “the cheapest ticket” - and specifically mentioned “I want a split ticket”. The clerk said it would cost £26.80 and that no split ticket arrangements would be cheaper.
With the 14.11 northern service to Crewe to depart in three minutes I was in no position to argue and reluctantly paid for two non split singles.
On the train I found out that splitting tickets at Wilmslow would appear to cost cost 17.80 plus 4.20. I appear to have been overcharged.
Thanks everybody in advance
Two questions arise:
1 Am I right on the fare calculations?
2 How do I complain about being mis sold my tickets?