changed all his statements)
what do you mean with "changed all his statements" please?
again i was charged by 0.000613 as mining charges, why i got charged again if i paid for 100 transactions already
Everytime you do a transaction, you pay mining fees (it does not matter how many transactions you did before). Basically. You pay for the amount of data using on the blockchain while doing your transaction.
You can set manually the fee or you can let Electrum or whatever tool you use, to set a price for you. Hope this clarifies your question?
And Yes, unfortunately, BTC transactions are just "One-Way-Fllight". In some cases, you have the possibility to pay more for the fees if your transaction is taking too long. But you will not be able to cancel a transaction.
Well, Paypal is not necessary secure, this is an other topic. Note that while BTC is decentralized, Paypal is centralized and they can anytime lock your funds, for whatever reason they have.
None place in the world is 100% secure. Nowadays, even with Escrow transaction, you can loose your money. Just be sure, wherever and whenever you are doing business, of what you are doing. That's all.