Too many sales calls

I’ve bought a car in the beginning of July. MFC is financing my car. Between 3 and 23 July I’ve received over 20 sales calls from them trying to sell more products to add to my monthly instalments. When I reject the offers they start to sound annoyed and are rude. I understand the need to do your job but this is just on another level. Let me pay my car instalments in peace, if I wanted all the extra stuff I would’ve asked for it!