paid for select seat

When I booked my holiday in February I paid extra for select seat(select seats mean you can seat together an selesct seat what you wont not paid an have just 2 choices). now is time to select my seat but I can't. I have medical cond.and can't seat on the window seat or midlle so i prefer to select midlle for my partner and aisle seat(always seat like that on my flight) for me but NO I CAN'T because they can't leave empty window seat. DON'T CARE ABOUT PEOPLE WITH MEDICAL COND. I SPOKE WITH CUSTOMER SERVICE AND THEY OFFER ME 2 AISLE SEAT BUT THIS MEAN I SEAT SEPERATE NOT TOGETHER WITH MY PARTNER. I FLOW WITH THOMSON BEFORE AND ALWAYS CAN SELECT SEAT WHAT I WON'T-now noT! So think,they should give info under the price when you book your holiday extras but there no ifo about just 2 poor choices what they give you!!!!!!!!!!!! well done thomson you are very poor service. i spoke with 5 people from customer service and just one men was nice and he lisen me.