Poor service delivery to customers

I purchased a barry more fishing bucket from basil manning which they carries a life time guarantee, I have sent it in previoulsy when I had problems and it was repaired, no questions asked ( look at your records BM) this time when I sent it because they could not fix it they told I had modified on my own, they are looking for every excuse not to honor the guarantee, they have even asked me for receipts from more than 5 years ago, I have purchased reels and rods from. BASIL MANNING SO I am not a once of customer, but they are not honoring there promise to the customer the sale rep advised me to purchase it cos of the guarantee yet they are looking reasons not to honor it, they need to go and looking the meaning of life time warranty,