Takelot sell tablet without serial no

In November 2014 I bought 2 x Dell Tablets 7inch from Takelot. In October 2015 the 1 did not want to charge anymore and contacted Takelot to send it back to them as it got 1 yr guarantee as per the call centre agent. I send the tablet back to only be told a week later that they can not assist me I must contact Dell direct. My husband went to Dell to get the item repaired. Dell told us that the Tablet do not have a serial no and therefore they can not assist me as it is dead and they can not even get the serial no from the tablet when it is on. I contacted Takelot and asked them why is there no serial no on the item as well as the box. They told me to send a mail and then later send the courier to collect the tablet. I was now again told they can not help me as they can not get the serial no!!! Now how do you sell an item to a client without a serial no and now make it the clients problem because without a serial no Dell will not accept the tablet to fix it. I bought the item from Takelot, I returned it within the warranty period to Takelot and was told they can not help, what is the value of a warranty period if Takelot do not honour it????Takelot what are you going to do???