Wow, I'm impressed by all the responses and kindness of everyone that responded. Thank you all so much, you are amazing people.
To address the questions raised. I bought anything between 500 and 1500 BTC back in 2009 or 2010, can't remember  the amount exactly. I downloaded electrum on my PC, and spent a couple of days teaching myself to transfer between wallets. I wrote down the seed words for each wallet in a note book and once I was successful in making a few transfers I totally forgot about Bitcoin; until 2016 when the price of Bitcoin started rallying like crazy.

Then I spent 5 years searching for the notebook and eventually found it. I restored the wallet but it was empty and showed no transactions ever taking place in the history. That is still the case with that wallet. Then yesterday I was paging through a notebook, for a novel I wrote (Two River Farm and the Cry of the Jackal if anyone is interested); and here I found another set of 12 words. I promptly plugged them into electrum and was pleasantly surprised  to see historical transactions on it; but depressed to see the balance as zero BTC.

Since the chances of someone else having the same seed as me as virtually zero, I can only imagine a scammer; somehow got hold of my seed, quite possible as I was using a windows XP laptop at the time and withdrew all my Bitcoin.
I think I'm in way over my head here; despite more than five years of searching.

Here is one of the transactions, see what you make of it and let me know.49b17aaeb9308d2d314438baf6321033af09f62c0e9914e5b01ac4d7ba481a4d  bc1qmuuc762cw02gg9j7fmqrw0wcmr0ffm5xkxjnln          10.78134

Either my money has been stolen or we've found the first ever key collision in the history of Bitcoin and that's worth the Bitcoin Foundation paying off my kids' student loans and some.

Any comments are fully appreciated.