Shocking aftersales

We bought over £800 of shower products from Bigbathroom, the tling in our bathroom was delayed due to delivery of tiles and when our plumbers came to fit the cubicle it was over hung the tray by 3mm. In the cubicle fitting instructions it says the tray lip must be a minimum of 70mm the tray the sent was only 65mm,if it was 70mm it would have fitted. After contacting Bigbathroom and explaing the problem we had we were told our money back date was out by 6 days,we explained we only wanted to exchange for a cubicle that would fit and were told bluntly,no returns or exchanges so we would have to keep the original one and purchase a new one.
We accept we were out of our refund date but no compassion,help or compromise were offered. This place should be avoided at all costs awful aftersales customer care that just wants to take your money and sell you products that don't have manufacturers given measurements.
Avoid at all costs.