Hello & welcome,
You have written here that even after cleaning your teeth twice daily, still they are not much clean. I think this might be related to your sensitivity though indirectly.
Failure to clean the oral cavity properly leads to accumulation of the plaque
along the gingival line on tooth surface & after a few days or months this causes gingiva to recess from it's natural position to somewhat at lower position.
If gingiva recesses to lower position,then root surface gets exposed thereby sensitivity develops which is painful ,too.
Plaque accumulation along with food debris collection is responsible for development of caries especially in the cervical region of the tooth.
Now, if this cervical caries
have not crossed the dentine to reach the pulp of the tooth, then Composite filling can be done by your dentist
But if the caries have reached the pulp tissue or even sensitivity is severe in the same teeth, Root canal treatment
is to be done followed by placement of crown.
Visit your dentist, get your teeth cleaned & checked clinically. And definitely you can go with your dentist's choice of treatment otherwise you have to take second opinion
to confirm the diagnosis.