Left in to dealer to get new battery and new seal

Question

about a week ago,i left my t90.4.496.51 tissot watch in to an official tissot dealer to get battery changed and also to have it sealed.i have owned the watch for less than 2 years.i have been in the sea.swimming pool shower etc. with it on and never had a problem with it. so to my amazement when i went swimming having got my watch back from the dealer there was condensation in the face! i was lead to believe these watches were water resistant for 50 metres! to my horror when i went back to the dealer he said that they were just water resisant for showers washing dishes etc. consequently my watch winder has rusted and needs replacing and the dealer expects me to pay for this! could you please let me know if this watch is totally waterproof for deep water
or is the dealer just winding me up! i was also wondering what a tissot warranty looks like.is it just the little booklet that came with the watch . thank you for listening and can you give me some answers ! yours faithfully sean pilkington ireland