Overcharging me

I have notice on quite a few occasions makro has been overcharging me for things in the last for months I have spent over 10000 in shop an online purchases all together specifically going into the store in ottery I can confidently say that when purchasing price is one thing for example my frimax string chips either 14.99 or 15.99 but when I got home an checked my slip it's 24.75 quite the price an it's not even lays I have experience this now on 2 other occasion I just through slip away but I see this is a constant thing of this store