You are incorrect. You can double spend a transaction which is not RBF enabled, it will just be slightly harder to do as less nodes will relay it, but it is still possible. It has been done multiple times in the past by other users in the same situation of the OP and I have done it before to prove that it could be done.
Ok. Here is my first transaction (non-RBF)
https://blockchain.info/tx/8ec829670f3e20f76155cc25a0dd91e5e4c6cdcfb19ba92aa2db44bde437d993 which pays a fee of barely above 10 sat/B
Here is the raw of my second RBF enabled transaction:
0100000001d13268bf354efa3afb1e36de03e22d4f7267ba85f2f0fb531efc09808a3b6d5f000000008b483045022100dbd5f4e2e8f38efba47d150048f2b4ab9ea81b46e2de3a0ae0d57f1a53f8eff802201adba6cf8c5e5aeb6b4a82734dbb58bb98aaef2eb1115a8e9d79cba991265d96014104d41dd0e449372f8896755cc74f0ed86cbfdffa531808dd4a391e09c3b9f629b98a12fd07487ed576131169fdceea9137909655aa079eb2a7eebd05742ab8d87afdffffff01c0732600000000001976a9147c298d5d195cf7ba257cff786e56026baf4a43a988ac00000000
Which pays a fee of 223 sat/B. Good luck double-spending my first tx with the second one, are there really some full RBF miners?
Yes, there are full RBF miners. I have done a double spend publicly on reddit:
https://www.reddit.com/r/btc/comments/5ar9sb/does_replace_by_fee_make_double_spending_easier/d9ivqtd/ Furthermore, how do you think everyone else who has stuck transaction issues are able to make a new transaction with a higher fee? They are double spending; they are making an RBF transaction without any RBF signalling in the original transaction. Seriously, take a look through the tech support section and look at all of the transactions people are complaining about. All of those transactions don't signal RBF and many of them are not confirmed but rather have been successfully double spent.
Anyways, this is off topic for this thread. Just because you do not understand how it works or why it works does not mean that it does not work. This has been done multiple times in the past; just because you don't know that does not mean that it does not work.
So, anymore things I can do now?
I had contacted Quickseller and macbook-air.
Thank you very much to all of you.
All you can do is wait. You can wait for the transaction to either confirm, or for it to eventually be "forgotten" by the network. In the latter case, the transaction should disappear from most block explorers and your wallet so you can just send the Bitcoin again but with a higher transaction fee. However for this to happen you have to wait a few days.