In the sitemap, url addresses are incorrectly created, & changes to; will it index the search engine correctly?

Question

Search Engine Optimization

Good afternoon!
The site is indexed very poorly, I noticed such a thing. In the sitemap file, page links have been slightly changed, the "&" symbol has been replaced with ";" , the page does not open on the new link, it swears that there is no such page, when I replaced the symbol back with my hands, Yandex and Google began to swear when checking
the sitemap . =product/category&p...
the link to the page is homestudio96.ru/index.php?route=product/category&a...
Tell me , maybe this is a jamb with indexing, the main pages were indexed on August 18 and have not been updated yet.

Answer 1

Put any simple free sitemap module on your opencart, write a line in robots and don't worry.
Or run again through the same service and do not change anything in the addresses. He's fine, as far as I remember.
Only Last modification check none.
In robots.txt, in any case, write down the address to the simap.

Answer 2

I did it via googlesitemap + added a rule to open the sitemap through the standard address /sitemap.xml , but Yandex swears at this sitemap
Error in XML
Line 3: XML declaration allowed only at the start of the document
Is this normal for opencart ?