delivery fees

i bought goods at a store that falls under Lewis group, i drove the goods to my house in my own car and was still charged for delivery fees, but the best is that the contract is printed out with the installment amount PRINTED ON THE CONTRACT then just under that is another amount which is slightly more than that written in pen without my or any of the staff''s signature next to it, in my mind this contract is now invalid as this is ***** and i will be seeking legal advise on this issue.