Don't give up, exhaust all possibilities. Did you follow the steps i told you to do?
Just so you know...I attempted your solution with Electrum-LTC on behalf of davedee to rule out a similar issue... However, the LTC "M" address matching the "3" address that davedee sent BTC funds to (found using this converter https://litecoin-project.github.io/p2sh-convert/), does not appear in the list of addresses generated in Electrum-LTC...
Another interesting point is that the seed mnemonic davedee has is actually recognised as a "SegWit" seed by Electrum... Even though it is supposedly a BIP39 seed generated by a Trezor??!?
This leads me to believe that, at least in davedee's case, the seed they have written down is actually an Electrum seed... and not the actual seed from their Trezor that generated the "3".
