We lived in a flat for seven years, paying the rent every month without fail. When we moved out we gave two months’ notice in writing stating we would leave the keys with a neighbour, however in March we got a solicitor’s letter saying the landlord hadn’t received our written notice and demanding three months’ rent.
Assuming you were entitled to end the tenancy on two months’ notice a court would have to decide whether or not you actually sent the letter to your landlord. Your unblemished payment record would no doubt be taken into account. I take it you used your deposit in lieu of paying your final months rent, which should have given your landlord advance warning of your intentions. If you receive a County Court claim you should contest it.